https://github.com/rakibul263/mysql-database
đ SQL-āĻāĻ° āĻā§āĻāĻāĻŋāĻ¨āĻžāĻāĻŋ (MySQL āĻ¸āĻš) āĻāĻ đī¸ āĻ°ā§āĻĒā§āĻāĻŋāĻāĻ°āĻŋāĻ¤ā§ SQL-āĻāĻ° āĻŦāĻŋāĻāĻŋāĻ¨ā§āĻ¨ āĻā§āĻāĻāĻŋāĻ¨āĻžāĻāĻŋ āĻŦāĻŋāĻˇā§ āĻŦāĻžāĻāĻ˛āĻž āĻāĻžāĻˇāĻžā§ đ āĻŦā§āĻ¯āĻžāĻā§āĻ¯āĻž āĻāĻ°āĻž āĻšā§ā§āĻā§āĨ¤ āĻāĻāĻžāĻ¨ā§ đĸī¸ MySQL-āĻāĻ° āĻĒā§āĻ°ā§ā§āĻāĻ¨ā§ā§ āĻā§ā§ā§āĻ°āĻŋāĻā§āĻ˛ā§ āĻ¸āĻāĻ¯ā§āĻā§āĻ¤ āĻāĻ°āĻž āĻšā§ā§āĻā§ â
https://github.com/rakibul263/mysql-database
database mysql-database sql
Last synced: 8 months ago
JSON representation
đ SQL-āĻāĻ° āĻā§āĻāĻāĻŋāĻ¨āĻžāĻāĻŋ (MySQL āĻ¸āĻš) āĻāĻ đī¸ āĻ°ā§āĻĒā§āĻāĻŋāĻāĻ°āĻŋāĻ¤ā§ SQL-āĻāĻ° āĻŦāĻŋāĻāĻŋāĻ¨ā§āĻ¨ āĻā§āĻāĻāĻŋāĻ¨āĻžāĻāĻŋ āĻŦāĻŋāĻˇā§ āĻŦāĻžāĻāĻ˛āĻž āĻāĻžāĻˇāĻžā§ đ āĻŦā§āĻ¯āĻžāĻā§āĻ¯āĻž āĻāĻ°āĻž āĻšā§ā§āĻā§āĨ¤ āĻāĻāĻžāĻ¨ā§ đĸī¸ MySQL-āĻāĻ° āĻĒā§āĻ°ā§ā§āĻāĻ¨ā§ā§ āĻā§ā§ā§āĻ°āĻŋāĻā§āĻ˛ā§ āĻ¸āĻāĻ¯ā§āĻā§āĻ¤ āĻāĻ°āĻž āĻšā§ā§āĻā§ â
- Host: GitHub
- URL: https://github.com/rakibul263/mysql-database
- Owner: rakibul263
- Created: 2025-02-19T04:57:07.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2025-02-19T17:30:39.000Z (over 1 year ago)
- Last Synced: 2025-02-19T18:26:31.891Z (over 1 year ago)
- Topics: database, mysql-database, sql
- Homepage:
- Size: 49.8 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
All About MySQL
### **`CREATE TABLE` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `CREATE TABLE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§ **āĻāĻāĻāĻŋ āĻ¨āĻ¤ā§āĻ¨ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻ¤ā§**āĨ¤
---
## **â
`CREATE TABLE` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
CREATE TABLE table_name (
column1 datatype constraints,
column2 datatype constraints,
column3 datatype constraints,
...
);
```
đš **`table_name`** â āĻ¨āĻ¤ā§āĻ¨ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¨āĻžāĻŽ
đš **`column1, column2, ...`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ
đš **`datatype`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻāĻ¨ā§āĻ¯ āĻĄāĻžāĻāĻž āĻāĻžāĻāĻĒ (āĻ¯ā§āĻŽāĻ¨: `INT`, `VARCHAR`, `DATE`, `DECIMAL` āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)
đš **`constraints`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻ°ā§āĻ˛ (āĻ¯ā§āĻŽāĻ¨: `PRIMARY KEY`, `NOT NULL`, `UNIQUE` āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)
---
## **â
`employees` āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻž**
```sql
CREATE TABLE employees (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
department VARCHAR(30),
age INT CHECK (age >= 18),
salary DECIMAL(10,2),
join_date DATE
);
```
đš **`id`** â Primary Key (āĻ¸ā§āĻŦāĻ¯āĻŧāĻāĻā§āĻ°āĻŋāĻ¯āĻŧāĻāĻžāĻŦā§ ā§§, ā§¨, ā§Š... āĻšāĻŦā§)
đš **`name`** â āĻ¨āĻžāĻŽ (`VARCHAR(50)`, āĻāĻžāĻ˛āĻŋ āĻ°āĻžāĻāĻž āĻ¯āĻžāĻŦā§ āĻ¨āĻž)
đš **`department`** â āĻŦāĻŋāĻāĻžāĻ (`VARCHAR(30)`, āĻāĻžāĻ˛āĻŋ āĻ°āĻžāĻāĻž āĻ¯āĻžāĻŦā§)
đš **`age`** â āĻŦā§āĻ¸ (āĻāĻŽāĻĒāĻā§āĻˇā§ ā§§ā§Ž āĻšāĻ¤ā§ āĻšāĻŦā§)
đš **`salary`** â āĻŦā§āĻ¤āĻ¨ (`DECIMAL(10,2)` āĻ
āĻ°ā§āĻĨāĻžā§, ā§§ā§Ļ āĻĄāĻŋāĻāĻŋāĻā§āĻ° āĻŽāĻ§ā§āĻ¯ā§ ā§¨ āĻĄāĻŋāĻāĻŋāĻ āĻĻāĻļāĻŽāĻŋāĻā§āĻ° āĻĒāĻ°)
đš **`join_date`** â āĻ¯ā§āĻāĻĻāĻžāĻ¨ā§āĻ° āĻ¤āĻžāĻ°āĻŋāĻ
---
## **â
`CREATE TABLE`-āĻāĻ° āĻ¸āĻžāĻĨā§ āĻāĻ¨ā§āĻĄāĻŋāĻļāĻ¨ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž**
### **ā§§. āĻ¯āĻĻāĻŋ āĻā§āĻŦāĻŋāĻ˛āĻāĻŋ āĻāĻā§ āĻĨā§āĻā§āĻ āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻĄāĻŋāĻ˛āĻŋāĻ āĻāĻ°ā§ āĻ¨āĻ¤ā§āĻ¨ āĻāĻ°ā§ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§**
```sql
DROP TABLE IF EXISTS employees;
CREATE TABLE employees (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
department VARCHAR(30),
age INT CHECK (age >= 18),
salary DECIMAL(10,2),
join_date DATE
);
```
đš **`DROP TABLE IF EXISTS employees;`** â āĻ¯āĻĻāĻŋ `employees` āĻā§āĻŦāĻŋāĻ˛ āĻāĻā§ āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻŽā§āĻā§ āĻĢā§āĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻāĻ°ā§ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§
---
### **ā§¨. āĻ¯āĻĻāĻŋ āĻā§āĻŦāĻŋāĻ˛āĻāĻŋ āĻāĻā§ āĻĨā§āĻā§ āĻ¨āĻž āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§**
```sql
CREATE TABLE IF NOT EXISTS employees (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
department VARCHAR(30),
age INT CHECK (age >= 18),
salary DECIMAL(10,2),
join_date DATE
);
```
đš **`IF NOT EXISTS`** â āĻ¯āĻĻāĻŋ `employees` āĻā§āĻŦāĻŋāĻ˛ āĻ¨āĻž āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻāĻ°ā§ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§
---
### **`INSERT INTO` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `INSERT INTO` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§ **āĻā§āĻŦāĻŋāĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻĄāĻžāĻāĻž āĻ¸āĻāĻ¯ā§āĻā§āĻ¤ āĻāĻ°āĻ¤ā§**āĨ¤
---
## **â
`INSERT INTO` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);
```
đš **`table_name`** â āĻ¯ā§ āĻā§āĻŦāĻŋāĻ˛ā§ āĻĄāĻžāĻāĻž āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž āĻšāĻŦā§
đš **`column1, column2, ...`** â āĻ¯ā§ āĻāĻ˛āĻžāĻŽāĻā§āĻ˛ā§āĻ° āĻāĻ¨ā§āĻ¯ āĻĄāĻžāĻāĻž āĻĻā§āĻā§āĻž āĻšāĻŦā§
đš **`value1, value2, ...`** â āĻ¯ā§ āĻŽāĻžāĻ¨āĻā§āĻ˛ā§ āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻšāĻŦā§
---
## **â
`employees` āĻā§āĻŦāĻŋāĻ˛ā§ ā§¨ā§Ļ āĻāĻ¨ āĻāĻ°ā§āĻŽā§āĻ° āĻĄāĻžāĻāĻž āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž**
```sql
INSERT INTO employees (name, department, age, salary, join_date) VALUES
('Samiul', 'IT', 25, 50000.00, '2022-03-15'),
('Fahim', 'HR', 30, 45000.50, '2021-07-10'),
('Ayesha', 'Finance', 28, 55000.75, '2022-10-05'),
('Rifat', 'IT', 27, 48000.00, '2023-01-12'),
('Tanjim', 'Marketing', 29, 47000.00, '2022-06-20'),
('Nabila', 'HR', 26, 42000.00, '2023-04-11'),
('Hasib', 'IT', 31, 52000.50, '2021-09-14'),
('Jannat', 'Finance', 24, 51000.00, '2022-02-07'),
('Rakib', 'IT', 28, 50000.00, '2023-03-18'),
('Mou', 'Marketing', 27, 46000.00, '2022-12-05'),
('Sabbir', 'Finance', 29, 53000.00, '2021-08-25'),
('Raihan', 'HR', 32, 41000.00, '2022-07-17'),
('Shamim', 'IT', 26, 47000.50, '2023-05-21'),
('Jui', 'Marketing', 30, 49000.00, '2022-11-09'),
('Tarek', 'Finance', 28, 52000.00, '2021-06-30'),
('Afia', 'HR', 25, 43000.00, '2023-08-14'),
('Mamun', 'IT', 33, 54000.75, '2022-09-19'),
('Tanvir', 'Marketing', 27, 48000.00, '2023-02-22'),
('Faria', 'Finance', 26, 51000.00, '2022-04-16'),
('Mehedi', 'HR', 29, 45000.00, '2023-07-29');
```
đš āĻāĻāĻžāĻ¨ā§ **ā§¨ā§Ļ āĻāĻ¨ āĻāĻ°ā§āĻŽā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž āĻšā§ā§āĻā§**
đš **`id` āĻāĻ˛āĻžāĻŽ `AUTO_INCREMENT` āĻĨāĻžāĻāĻ˛ā§** āĻ¸ā§āĻāĻŋ āĻ¸ā§āĻŦāĻ¯āĻŧāĻāĻā§āĻ°āĻŋāĻ¯āĻŧāĻāĻžāĻŦā§ āĻ¸āĻāĻā§āĻ¯āĻž āĻ
ā§āĻ¯āĻžāĻ¸āĻžāĻāĻ¨ āĻāĻ°āĻŦā§
---
## **â
āĻ¸āĻŦ āĻāĻ˛āĻžāĻŽā§ āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž (āĻā§āĻ¨ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻāĻ˛āĻžāĻŽ āĻāĻ˛ā§āĻ˛ā§āĻ āĻ¨āĻž āĻāĻ°ā§)**
```sql
INSERT INTO employees VALUES
(21, 'Kamal', 'IT', 30, 52000.00, '2023-06-12');
```
đš **āĻ¸āĻŦ āĻāĻ˛āĻžāĻŽā§āĻ° āĻāĻ¨ā§āĻ¯ āĻŽāĻžāĻ¨ āĻĻāĻŋāĻ¤ā§ āĻšāĻŦā§**
đš **`id` āĻāĻ˛āĻžāĻŽā§ āĻ¸ā§āĻŦāĻ¯āĻŧāĻāĻā§āĻ°āĻŋāĻ¯āĻŧ āĻ¸āĻāĻā§āĻ¯āĻž āĻ¯ā§āĻā§āĻ¤ āĻšāĻ˛ā§ āĻĒā§āĻ°āĻĨāĻŽ āĻāĻ˛āĻžāĻŽ āĻŦāĻžāĻĻ āĻĻā§āĻā§āĻž āĻāĻāĻŋāĻ¤**
---
## **â
āĻāĻāĻžāĻ§āĻŋāĻ `INSERT` āĻāĻāĻ¸āĻžāĻĨā§ āĻāĻžāĻ˛āĻžāĻ¨ā§ (Bulk Insert)**
```sql
INSERT INTO employees (name, department, age, salary, join_date) VALUES
('Arif', 'IT', 28, 49000.00, '2023-01-05'),
('Mahin', 'Finance', 27, 53000.00, '2022-08-23'),
('Saima', 'HR', 26, 44000.00, '2023-10-10');
```
đš **āĻāĻāĻāĻŋ `INSERT INTO` āĻ¸ā§āĻā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻāĻžāĻ§āĻŋāĻ āĻ°ā§ āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž āĻ¯āĻžā§**
---
## **â
`INSERT` + `SELECT` (āĻ
āĻ¨ā§āĻ¯ āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ āĻĄāĻžāĻāĻž āĻāĻĒāĻŋ āĻāĻ°āĻž)**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ
āĻ¨ā§āĻ¯ āĻāĻāĻāĻŋ āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ āĻĄāĻžāĻāĻž āĻāĻĒāĻŋ āĻāĻ°ā§ `employees` āĻā§āĻŦāĻŋāĻ˛ā§ āĻ°āĻžāĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
INSERT INTO employees (name, department, age, salary, join_date)
SELECT full_name, dept, years, pay, start_date FROM old_employees;
```
đš āĻāĻāĻŋ **`old_employees` āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ āĻĄāĻžāĻāĻž āĻ¨āĻŋā§ā§ `employees` āĻā§āĻŦāĻŋāĻ˛ā§ āĻ¸āĻāĻ¯ā§āĻā§āĻ¤ āĻāĻ°āĻŦā§**
---
## **â
āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻžāĻ° āĻĒāĻ° āĻĄāĻžāĻāĻž āĻā§āĻ āĻāĻ°āĻž (`SELECT` āĻĻāĻŋā§ā§)**
```sql
SELECT * FROM employees;
```
đš **`employees` āĻā§āĻŦāĻŋāĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻ¯ā§āĻ āĻāĻ°āĻž āĻĄāĻžāĻāĻž āĻĻā§āĻāĻžāĻŦā§**
---
### **`UPDATE` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `UPDATE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§ **āĻ
āĻŦāĻ¸ā§āĻĨāĻžāĻ¨ā§ āĻĨāĻžāĻāĻž āĻĄāĻžāĻāĻž āĻĒāĻ°āĻŋāĻŦāĻ°ā§āĻ¤āĻ¨ āĻāĻ°āĻ¤ā§**āĨ¤
---
## **â
`UPDATE` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
```
đš **`table_name`** â āĻ¯ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻĄāĻžāĻāĻž āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻŦā§āĻ¨
đš **`SET`** â āĻ¯ā§āĻ¸āĻŦ āĻāĻ˛āĻžāĻŽā§āĻ° āĻŽāĻžāĻ¨ āĻĒāĻ°āĻŋāĻŦāĻ°ā§āĻ¤āĻ¨ āĻāĻ°āĻ¤ā§ āĻāĻžāĻ¨
đš **`WHERE`** â āĻā§āĻ¨ āĻ°ā§ (row) āĻāĻĒāĻĄā§āĻ āĻšāĻŦā§, āĻ¸ā§āĻāĻž āĻ āĻŋāĻ āĻāĻ°āĻ¤ā§
â ī¸ **IMPORTANT:**
**`WHERE` āĻ¨āĻž āĻĻāĻŋāĻ˛ā§ āĻĒā§āĻ°ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻĄāĻžāĻāĻž āĻāĻĒāĻĄā§āĻ āĻšā§ā§ āĻ¯āĻžāĻŦā§!** āĻ¸āĻžāĻŦāĻ§āĻžāĻ¨ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§āĻ¨āĨ¤
---
## **â
ā§§. āĻāĻ āĻāĻ˛āĻžāĻŽ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž**
āĻ§āĻ°āĻŋ, āĻāĻŽāĻ°āĻž **ID ā§§** āĻ¨āĻŽā§āĻŦāĻ° āĻāĻ°ā§āĻŽā§āĻ° āĻŦā§āĻ¤āĻ¨ āĻŦāĻžā§āĻŋā§ā§ **ā§Ŧā§Ļā§Ļā§Ļā§Ļ** āĻāĻ°āĻ¤ā§ āĻāĻžāĻ:
```sql
UPDATE employees
SET salary = 60000
WHERE id = 1;
```
đš **Result:** `id = 1` āĻāĻ° **`salary` 60000** āĻ āĻāĻĒāĻĄā§āĻ āĻšāĻŦā§āĨ¤
---
## **â
ā§¨. āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **ID ā§¨** āĻ¨āĻŽā§āĻŦāĻ° āĻāĻ°ā§āĻŽā§āĻ° **āĻŦā§āĻ¤āĻ¨ āĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ** āĻĒāĻ°āĻŋāĻŦāĻ°ā§āĻ¤āĻ¨ āĻāĻ°āĻ¤ā§ āĻāĻžāĻ:
```sql
UPDATE employees
SET salary = 48000, department = 'Marketing'
WHERE id = 2;
```
đš **Result:** `id = 2` āĻāĻ° **āĻŦā§āĻ¤āĻ¨** āĻāĻŦāĻ **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ** āĻāĻĒāĻĄā§āĻ āĻšāĻŦā§āĨ¤
---
## **â
ā§Š. āĻļāĻ°ā§āĻ¤ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻā§āĻ¨, āĻ¤āĻžāĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ ā§§ā§Ļ% āĻŦāĻžā§āĻžāĻ¤ā§ āĻāĻžāĻ**:
```sql
UPDATE employees
SET salary = salary * 1.10
WHERE department = 'IT';
```
đš **Result:** **IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§āĻ° āĻŦā§āĻ¤āĻ¨ ā§§ā§Ļ% āĻŦāĻžā§āĻŦā§āĨ¤**
---
## **â
ā§Ē. āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¤āĻžāĻ°āĻŋāĻā§āĻ° āĻāĻĒāĻ° āĻāĻŋāĻ¤ā§āĻ¤āĻŋ āĻāĻ°ā§ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž ā§¨ā§Ļā§¨ā§¨ āĻ¸āĻžāĻ˛ā§āĻ° āĻāĻā§ āĻā§ā§āĻ¨ āĻāĻ°ā§āĻā§, āĻ¤āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ 'Senior' āĻāĻ°āĻ¤ā§ āĻāĻžāĻ**:
```sql
UPDATE employees
SET department = 'Senior'
WHERE join_date < '2022-01-01';
```
đš **Result:** **ā§¨ā§Ļā§¨ā§¨ āĻ¸āĻžāĻ˛ā§āĻ° āĻāĻā§ āĻā§ā§āĻ¨ āĻāĻ°āĻž āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ 'Senior' āĻšāĻŦā§āĨ¤**
---
## **â
ā§Ģ. `UPDATE` āĻāĻ°āĻžāĻ° āĻĒāĻ° āĻĄāĻžāĻāĻž āĻā§āĻ āĻāĻ°āĻž (`SELECT`)**
```sql
SELECT * FROM employees;
```
đš **āĻāĻĒāĻĄā§āĻā§āĻĄ āĻĄāĻžāĻāĻž āĻĻā§āĻāĻžāĻ¨ā§āĻ° āĻāĻ¨ā§āĻ¯ `SELECT` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°ā§āĻ¨āĨ¤**
---
## **â
ā§Ŧ. `UPDATE` + `LIMIT` (āĻ¸ā§āĻŽāĻŋāĻ¤ āĻ°ā§ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž)**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻļā§āĻ§ā§ āĻĒā§āĻ°āĻĨāĻŽ ā§Ģ āĻāĻ¨ā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ 'Test' āĻāĻ°āĻ¤ā§ āĻāĻžāĻ**:
```sql
UPDATE employees
SET department = 'Test'
LIMIT 5;
```
đš **Result:** **āĻĒā§āĻ°āĻĨāĻŽ ā§Ģ āĻāĻ¨ āĻāĻ°ā§āĻŽā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ 'Test' āĻšāĻŦā§āĨ¤**
---
## **â
ā§. `UPDATE` + `ORDER BY` (āĻ¸āĻžāĻāĻŋā§ā§ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž)**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨ āĻŦā§āĻ¤āĻ¨ā§āĻ° āĻāĻ°ā§āĻŽā§āĻ° āĻŦā§āĻ¤āĻ¨ ā§Ēā§Ģā§Ļā§Ļā§Ļ āĻāĻ°āĻ¤ā§ āĻāĻžāĻ**:
```sql
UPDATE employees
SET salary = 45000
ORDER BY salary ASC
LIMIT 1;
```
đš **Result:** **āĻ¸āĻŦāĻā§ā§ā§ āĻāĻŽ āĻŦā§āĻ¤āĻ¨ āĻĒāĻžāĻā§āĻž āĻāĻ°ā§āĻŽā§āĻ° āĻŦā§āĻ¤āĻ¨ ā§Ēā§Ģā§Ļā§Ļā§Ļ āĻšāĻŦā§āĨ¤**
---
## **â
āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `UPDATE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻžāĻ° āĻ¸ā§āĻŦāĻŋāĻ§āĻž**
â **āĻĄāĻžāĻāĻž āĻ¸āĻšāĻā§ āĻĒāĻ°āĻŋāĻŦāĻ°ā§āĻ¤āĻ¨ āĻāĻ°āĻž āĻ¯āĻžā§**
â **āĻļāĻ°ā§āĻ¤ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ°ā§ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž āĻ¯āĻžā§**
â **āĻāĻžāĻŖāĻŋāĻ¤āĻŋāĻ āĻ
āĻĒāĻžāĻ°ā§āĻļāĻ¨ (āĻ¯ā§āĻŽāĻ¨: `salary * 1.10`) āĻāĻ°āĻž āĻ¯āĻžā§**
### **`WHERE` Clause āĻāĻŋ āĻāĻŦāĻ āĻāĻāĻŋ āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
`WHERE` āĻā§āĻ˛āĻ SQL-āĻ¤ā§ **āĻļāĻ°ā§āĻ¤ āĻ¨āĻŋāĻ°ā§āĻ§āĻžāĻ°āĻŖā§āĻ° āĻāĻ¨ā§āĻ¯ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšāĻ¯āĻŧ**āĨ¤ āĻ¯āĻāĻ¨ āĻāĻŽāĻ°āĻž āĻā§āĻ¨ā§ āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ **āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻĄā§āĻāĻž āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ°** āĻāĻ°āĻ¤ā§ āĻāĻžāĻ, āĻ¤āĻāĻ¨ `WHERE` āĻā§āĻ˛āĻ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧāĨ¤ āĻāĻāĻŋ āĻŽā§āĻ˛āĻ¤ `SELECT`, `UPDATE`, `DELETE` āĻāĻŦāĻ `INSERT` āĻ¸ā§āĻā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧāĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§§: āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°āĻž**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻŽāĻ°āĻž `IT` āĻŦāĻŋāĻāĻžāĻā§ āĻāĻ°ā§āĻŽāĻ°āĻ¤ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĨ¤
```sql
SELECT * FROM Employees WHERE department = 'IT';
```
đ āĻāĻ āĻāĻŋāĻāĻ°āĻŋāĻāĻŋ `Employees` āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° `IT` āĻŦāĻŋāĻāĻžāĻā§ āĻāĻžāĻ āĻāĻ°āĻž āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§¨: ā§Šā§Ļ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ āĻŦāĻ¯āĻŧāĻ¸ā§ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻ¤āĻžāĻ˛āĻŋāĻāĻž**
```sql
SELECT * FROM Employees WHERE age > 30;
```
đ āĻāĻ āĻāĻŋāĻāĻ°āĻŋ āĻ¸ā§āĻāĻ¸āĻŦ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĻā§āĻāĻžāĻŦā§ āĻ¯āĻžāĻĻā§āĻ° āĻŦāĻ¯āĻŧāĻ¸ **ā§Šā§Ļ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ**āĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§Š: āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻŦā§āĻ¤āĻ¨āĻ¸ā§āĻŽāĻžāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻ¤āĻžāĻ˛āĻŋāĻāĻž**
āĻ§āĻ°āĻŋ, āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ āĻ¯āĻžāĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ **ā§Ēā§Ļā§Ļā§Ļā§Ļ āĻĨā§āĻā§ ā§Ģā§Ļā§Ļā§Ļā§Ļ** āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§āĨ¤
```sql
SELECT * FROM Employees WHERE salary BETWEEN 40000 AND 50000;
```
đ āĻāĻ āĻāĻŋāĻāĻ°āĻŋ āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§ āĻ¯āĻžāĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ ā§Ēā§Ļā§Ļā§Ļā§Ļ āĻĨā§āĻā§ ā§Ģā§Ļā§Ļā§Ļā§Ļ āĻāĻžāĻāĻžāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻāĻā§āĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§Ē: `HR` āĻŦāĻŋāĻāĻžāĻ āĻŦāĻžāĻĻā§ āĻ
āĻ¨ā§āĻ¯āĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯**
āĻāĻŽāĻ°āĻž āĻ¯āĻĻāĻŋ `HR` āĻŦāĻŋāĻāĻžāĻā§āĻ° āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻŦāĻžāĻĻ āĻĻāĻŋāĻ¯āĻŧā§ āĻŦāĻžāĻāĻŋ āĻ¸āĻāĻ˛āĻā§ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ:
```sql
SELECT * FROM Employees WHERE department <> 'HR';
```
(āĻāĻāĻžāĻ¨ā§ `<>` āĻ
āĻ°ā§āĻĨ **"āĻ¸āĻŽāĻžāĻ¨ āĻ¨āĻ¯āĻŧ"**)
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§Ģ: ā§¨ā§Ļā§¨ā§§ āĻ¸āĻžāĻ˛ā§āĻ° āĻĒāĻ°ā§ āĻ¯ā§āĻ āĻĻā§āĻāĻ¯āĻŧāĻž āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻ°āĻž**
```sql
SELECT * FROM Employees WHERE join_date > '2021-12-31';
```
đ āĻāĻ āĻāĻŋāĻāĻ°āĻŋāĻāĻŋ **ā§¨ā§Ļā§¨ā§¨ āĻŦāĻž āĻāĻ° āĻĒāĻ°ā§** āĻ¯ā§āĻ āĻĻā§āĻāĻ¯āĻŧāĻž āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§Ŧ: āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¨āĻžāĻŽā§ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§ āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž `Rahim Islam` āĻ¨āĻžāĻŽā§āĻ° āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻāĻžāĻ¨āĻ¤ā§ āĻāĻžāĻ:
```sql
SELECT * FROM Employees WHERE name = 'Rahim Islam';
```
đ āĻāĻāĻŋ āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° **Rahim Islam**-āĻāĻ° āĻ¤āĻĨā§āĻ¯ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§: āĻāĻāĻžāĻ§āĻŋāĻ āĻļāĻ°ā§āĻ¤ āĻāĻāĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž (`AND` āĻāĻŦāĻ `OR`)**
â
**āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž `IT` āĻŦāĻŋāĻāĻžāĻā§āĻ° āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ āĻ¯āĻžāĻĻā§āĻ° āĻŦāĻ¯āĻŧāĻ¸ ā§¨ā§Ģ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ:**
```sql
SELECT * FROM Employees WHERE department = 'IT' AND age > 25;
```
đ āĻāĻāĻŋ āĻļā§āĻ§ā§ `IT` āĻŦāĻŋāĻāĻžāĻā§āĻ° **āĻ¯āĻžāĻĻā§āĻ° āĻŦāĻ¯āĻŧāĻ¸ ā§¨ā§Ģ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ** āĻ¤āĻžāĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĻā§āĻāĻžāĻŦā§āĨ¤
â
**āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž `HR` āĻŦāĻž `Finance` āĻŦāĻŋāĻāĻžāĻā§āĻ° āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ:**
```sql
SELECT * FROM Employees WHERE department = 'HR' OR department = 'Finance';
```
đ āĻāĻāĻŋ `HR` āĻāĻŦāĻ `Finance` āĻŦāĻŋāĻāĻžāĻā§ āĻāĻ°ā§āĻŽāĻ°āĻ¤ āĻ¸āĻāĻ˛ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **āĻāĻĒāĻ¸āĻāĻšāĻžāĻ°**
đš `WHERE` āĻā§āĻ˛āĻ **āĻĄāĻžāĻāĻžāĻŦā§āĻ āĻĨā§āĻā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻĄā§āĻāĻž āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻ¸āĻžāĻšāĻžāĻ¯ā§āĻ¯ āĻāĻ°ā§**āĨ¤
đš āĻāĻāĻŋ `=`, `>`, `<`, `>=`, `<=`, `<>`, `BETWEEN`, `AND`, `OR` āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ āĻ
āĻĒāĻžāĻ°ā§āĻāĻ°ā§āĻ° āĻŽāĻžāĻ§ā§āĻ¯āĻŽā§ āĻāĻžāĻ āĻāĻ°ā§āĨ¤
đš āĻāĻŽāĻ°āĻž `WHERE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻŦāĻŋāĻāĻžāĻ, āĻŦāĻ¯āĻŧāĻ¸, āĻŦā§āĻ¤āĻ¨, āĻ¯ā§āĻāĻĻāĻžāĻ¨ā§āĻ° āĻ¤āĻžāĻ°āĻŋāĻ āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋāĻ° āĻāĻŋāĻ¤ā§āĻ¤āĻŋāĻ¤ā§ āĻāĻ°ā§āĻŽāĻāĻžāĻ°ā§āĻĻā§āĻ° āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°āĻŋāĨ¤
### **`BETWEEN` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
`BETWEEN` **āĻĻā§āĻāĻŋ āĻŽāĻžāĻ¨ā§āĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻĄāĻžāĻāĻž āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°āĻ¤ā§** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧāĨ¤ āĻāĻāĻŋ **inclusive**, āĻ
āĻ°ā§āĻĨāĻžā§ **āĻļā§āĻ°ā§āĻ° āĻŽāĻžāĻ¨ āĻ āĻļā§āĻˇā§āĻ° āĻŽāĻžāĻ¨ āĻĻā§āĻā§āĻ āĻ
āĻ¨ā§āĻ¤āĻ°ā§āĻā§āĻā§āĻ¤ āĻāĻ°ā§**āĨ¤
#### **āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
SELECT column_name FROM table_name
WHERE column_name BETWEEN value1 AND value2;
```
āĻāĻāĻžāĻ¨ā§ `value1` āĻāĻŦāĻ `value2` āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻĨāĻžāĻāĻž āĻ¸āĻŦ āĻĄāĻžāĻāĻž **āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨** āĻāĻ°āĻŦā§āĨ¤
---
### ***āĻĒā§āĻ°ā§āĻ¯āĻžāĻāĻāĻŋāĻā§āĻ¯āĻžāĻ˛ āĻāĻĻāĻžāĻšāĻ°āĻŖ***
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻŽāĻ°āĻž `Employees` āĻā§āĻŦāĻŋāĻ˛ āĻĨā§āĻā§ **āĻ¯āĻžāĻ°āĻž ā§Ēā§Ļ,ā§Ļā§Ļā§Ļ āĻĨā§āĻā§ ā§Ģā§Ļ,ā§Ļā§Ļā§Ļ āĻāĻžāĻāĻžāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻŦā§āĻ¤āĻ¨ āĻĒāĻžāĻ¯āĻŧ āĻ¤āĻžāĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE salary BETWEEN 40000 AND 50000;
```
āĻāĻāĻŋ **ā§Ēā§Ļ,ā§Ļā§Ļā§Ļ āĻĨā§āĻā§ ā§Ģā§Ļ,ā§Ļā§Ļā§Ļ āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻĨāĻžāĻāĻž āĻ¸āĻāĻ˛ salary** āĻ¸āĻš employee āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **āĻ¤āĻžāĻ°āĻŋāĻā§āĻ° āĻāĻ¨ā§āĻ¯ `BETWEEN` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
āĻ§āĻ°ā§āĻ¨, āĻāĻŽāĻ°āĻž ā§¨ā§Ļā§¨ā§¨ āĻ¸āĻžāĻ˛ā§āĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻāĻ¯āĻŧā§āĻ¨ āĻāĻ°āĻž āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ:
```sql
SELECT * FROM Employees
WHERE join_date BETWEEN '2022-01-01' AND '2022-12-31';
```
āĻāĻāĻžāĻ¨ā§, **`join_date` āĻ¯āĻĻāĻŋ ā§§āĻ˛āĻž āĻāĻžāĻ¨ā§āĻ¯āĻŧāĻžāĻ°āĻŋ ā§¨ā§Ļā§¨ā§¨ āĻĨā§āĻā§ ā§Šā§§āĻļā§ āĻĄāĻŋāĻ¸ā§āĻŽā§āĻŦāĻ° ā§¨ā§Ļā§¨ā§¨ āĻāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻĒāĻĄāĻŧā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¸ā§āĻ āĻ¸āĻŦ āĻ°ā§ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§**āĨ¤
---
### **`BETWEEN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻžāĻ° āĻ¸ā§āĻŦāĻŋāĻ§āĻž:**
â
**āĻā§āĻĄ āĻā§āĻ āĻšāĻ¯āĻŧ** â `BETWEEN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ āĻ¸āĻšāĻā§āĻ āĻ°ā§āĻā§āĻ āĻ¸ā§āĻ āĻāĻ°āĻž āĻ¯āĻžāĻ¯āĻŧ
â
**āĻĒāĻžāĻ°āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻ¨ā§āĻ¸ āĻāĻžāĻ˛ā§ āĻšāĻ¯āĻŧ** â āĻāĻāĻŋ **āĻāĻ¨ā§āĻĄā§āĻā§āĻ¸** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻāĻžāĻ°ā§āĻ¯āĻāĻ°āĻāĻžāĻŦā§ āĻĄāĻžāĻāĻž āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°ā§
â
**āĻŦā§āĻāĻ¤ā§ āĻ¸āĻšāĻ** â āĻāĻāĻŋ `>=` āĻāĻŦāĻ `<=` āĻāĻ° āĻ¸āĻŽāĻ¤ā§āĻ˛ā§āĻ¯, āĻ¤āĻŦā§ āĻāĻŽ āĻāĻāĻŋāĻ˛
---
### **`BETWEEN` āĻāĻ° āĻŦāĻŋāĻāĻ˛ā§āĻĒ (`>=` āĻāĻŦāĻ `<=`)**
āĻāĻĒāĻ°ā§ āĻĻā§āĻāĻ¯āĻŧāĻž query āĻ¨āĻŋāĻā§āĻ° āĻŽāĻ¤ āĻāĻ°ā§āĻ āĻ˛ā§āĻāĻž āĻ¯āĻžāĻ¯āĻŧ:
```sql
SELECT * FROM Employees
WHERE salary >= 40000 AND salary <= 50000;
```
āĻāĻŋāĻ¨ā§āĻ¤ā§ **`BETWEEN` āĻāĻŽāĻĒā§āĻ¯āĻžāĻā§āĻ āĻāĻŦāĻ āĻ¸āĻšāĻāĻŦā§āĻ§ā§āĻ¯**, āĻ¤āĻžāĻ āĻāĻāĻŋāĻ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšāĻ¯āĻŧāĨ¤
### **`IN` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `IN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧ **āĻāĻāĻāĻŋ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¤āĻžāĻ˛āĻŋāĻāĻžāĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻĨāĻžāĻāĻž āĻŽāĻžāĻ¨āĻā§āĻ˛ā§āĻ° āĻ¸āĻžāĻĨā§ āĻŽāĻŋāĻ˛ āĻāĻā§ āĻāĻŋāĻ¨āĻž āĻ¤āĻž āĻā§āĻ āĻāĻ°āĻ¤ā§**āĨ¤ āĻāĻāĻŋ `OR` āĻāĻ¨ā§āĻĄāĻŋāĻļāĻ¨ā§āĻ° āĻ¸āĻšāĻāĻ¤āĻ° āĻŦāĻŋāĻāĻ˛ā§āĻĒāĨ¤
---
### **āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
SELECT column_name FROM table_name
WHERE column_name IN (value1, value2, value3, ...);
```
āĻāĻāĻŋ **`column_name` āĻ¯āĻĻāĻŋ `value1`, `value2`, āĻŦāĻž `value3` āĻāĻ° āĻā§āĻ¨ā§ āĻāĻāĻāĻŋāĻ° āĻ¸āĻŽāĻžāĻ¨ āĻšāĻ¯āĻŧ, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¸ā§āĻ āĻ°ā§ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§**āĨ¤
---
### **āĻĒā§āĻ°ā§āĻ¯āĻžāĻāĻāĻŋāĻā§āĻ¯āĻžāĻ˛ āĻāĻĻāĻžāĻšāĻ°āĻŖ**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻŽāĻ°āĻž **"HR", "IT", āĻāĻŦāĻ "Finance"** āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻāĨ¤
â
**`IN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§:**
```sql
SELECT * FROM Employees
WHERE department IN ('HR', 'IT', 'Finance');
```
āĻāĻāĻŋ **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° HR, IT, āĻāĻŦāĻ Finance āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ°ā§āĻāĻ°ā§āĻĄ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§**āĨ¤
â **`OR` āĻĻāĻŋāĻ¯āĻŧā§ āĻāĻ°āĻ˛ā§:**
```sql
SELECT * FROM Employees
WHERE department = 'HR' OR department = 'IT' OR department = 'Finance';
```
`IN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ āĻā§āĻĄ āĻā§āĻ āĻāĻŦāĻ āĻ¸āĻšāĻ āĻšāĻ¯āĻŧā§ āĻ¯āĻžāĻ¯āĻŧāĨ¤
---
### **`IN` āĻ¸āĻāĻā§āĻ¯āĻž āĻŦāĻž āĻ¤āĻžāĻ°āĻŋāĻā§āĻ° āĻ¸āĻžāĻĨā§āĻ āĻāĻžāĻ āĻāĻ°ā§**
āĻāĻŽāĻ°āĻž āĻ¯āĻĻāĻŋ **āĻ¯āĻžāĻ°āĻž ā§¨ā§Ģ, ā§Šā§Ļ, āĻ
āĻĨāĻŦāĻž ā§Šā§Ģ āĻŦāĻāĻ° āĻŦāĻ¯āĻŧāĻ¸ā§ āĻ¤āĻžāĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ**, āĻ¤āĻžāĻšāĻ˛ā§:
```sql
SELECT * FROM Employees
WHERE age IN (25, 30, 35);
```
āĻāĻāĻŋ **ā§¨ā§Ģ, ā§Šā§Ļ āĻŦāĻž ā§Šā§Ģ āĻŦāĻāĻ° āĻŦāĻ¯āĻŧāĻ¸ā§ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§**āĨ¤
āĻ¤āĻžāĻ°āĻŋāĻā§āĻ° āĻā§āĻˇā§āĻ¤ā§āĻ°ā§āĻ āĻāĻžāĻ āĻāĻ°ā§:
```sql
SELECT * FROM Employees
WHERE join_date IN ('2022-01-10', '2023-04-18', '2021-07-01');
```
āĻāĻāĻŋ āĻļā§āĻ§ā§ **āĻāĻ āĻ¤āĻŋāĻ¨āĻāĻŋ āĻ¤āĻžāĻ°āĻŋāĻā§ āĻāĻ¯āĻŧā§āĻ¨ āĻāĻ°āĻž āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**āĨ¤
---
### **`IN` āĻāĻŦāĻ `NOT IN`**
#### â
**`IN` â āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻŽāĻžāĻ¨āĻā§āĻ˛ā§āĻā§ āĻ
āĻ¨ā§āĻ¤āĻ°ā§āĻā§āĻā§āĻ¤ āĻāĻ°ā§**
```sql
SELECT * FROM Employees
WHERE department IN ('IT', 'Finance');
```
āĻāĻāĻŋ **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° IT āĻāĻŦāĻ Finance āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**āĨ¤
#### â **`NOT IN` â āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻŽāĻžāĻ¨āĻā§āĻ˛ā§ āĻŦāĻžāĻĻ āĻĻā§āĻ¯āĻŧ**
```sql
SELECT * FROM Employees
WHERE department NOT IN ('IT', 'Finance');
```
āĻāĻāĻŋ **IT āĻāĻŦāĻ Finance āĻŦāĻžāĻĻ āĻĻāĻŋāĻ¯āĻŧā§ āĻŦāĻžāĻāĻŋ āĻ¸āĻŦ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**āĨ¤
---
### **`IN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻžāĻ° āĻ¸ā§āĻŦāĻŋāĻ§āĻž**
â
**āĻā§āĻĄ āĻā§āĻ āĻšāĻ¯āĻŧ** â `IN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ `OR` āĻŦāĻžāĻ°āĻŦāĻžāĻ° āĻ˛āĻŋāĻāĻ¤ā§ āĻšāĻ¯āĻŧ āĻ¨āĻž
â
**āĻĒāĻžāĻ°āĻĢāĻ°āĻŽā§āĻ¯āĻžāĻ¨ā§āĻ¸ āĻāĻžāĻ˛ā§ āĻšāĻ¤ā§ āĻĒāĻžāĻ°ā§** â āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻŽāĻžāĻ¨āĻā§āĻ˛ā§āĻ° āĻāĻ¨ā§āĻ¯ **āĻāĻ¨āĻĄā§āĻā§āĻ¸** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻĻā§āĻ°ā§āĻ¤ āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžāĻ¯āĻŧ
â
**āĻŦā§āĻāĻž āĻ¸āĻšāĻ** â āĻāĻāĻžāĻ§āĻŋāĻ āĻŽāĻžāĻ¨ āĻā§āĻ āĻāĻ°āĻžāĻ° āĻ¸āĻšāĻāĻ¤āĻ° āĻāĻĒāĻžāĻ¯āĻŧ
### **`LIKE` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `LIKE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧ **āĻĒā§āĻ¯āĻžāĻāĻžāĻ°ā§āĻ¨ āĻŽāĻŋāĻ˛āĻŋāĻ¯āĻŧā§ (pattern matching) āĻĄāĻžāĻāĻž āĻā§āĻāĻāĻ¤ā§**āĨ¤ āĻāĻāĻŋ **`WHERE`-āĻāĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧ** āĻāĻŦāĻ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ **`%` āĻ `_` wildcard** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšāĻ¯āĻŧāĨ¤
---
## **â
`LIKE` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
SELECT column_name FROM table_name
WHERE column_name LIKE 'pattern';
```
āĻāĻāĻžāĻ¨ā§ **`pattern` āĻŽāĻžāĻ¨ā§āĻ° āĻ¸āĻžāĻĨā§ āĻŽāĻŋāĻ˛āĻ˛ā§ āĻ¸ā§āĻ āĻ°ā§ āĻā§āĻ˛ā§ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻšāĻŦā§āĨ¤**
---
## **đš `LIKE`-āĻ Wildcard āĻā§āĻ˛ā§ āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
| Wildcard | āĻāĻžāĻ |
|----------|------------------------------------------------|
| `%` | **āĻļā§āĻ¨ā§āĻ¯ āĻŦāĻž āĻ¯ā§āĻā§āĻ¨ā§ āĻ¸āĻāĻā§āĻ¯āĻ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ°** āĻ°āĻŋāĻĒā§āĻ°ā§āĻā§āĻ¨ā§āĻ āĻāĻ°ā§ |
| `_` | **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° ā§§āĻāĻŋ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ°** āĻ°āĻŋāĻĒā§āĻ°ā§āĻā§āĻ¨ā§āĻ āĻāĻ°ā§ |
---
## **đ¸ `%` Wildcard āĻĻāĻŋāĻ¯āĻŧā§ āĻāĻĻāĻžāĻšāĻ°āĻŖ**
### **ā§§ī¸âŖ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ
āĻā§āĻˇāĻ° āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§ āĻšāĻāĻ¯āĻŧāĻž āĻĄāĻžāĻāĻž āĻā§āĻāĻāĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽ 'S' āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§ āĻšāĻ¯āĻŧā§āĻā§**
```sql
SELECT * FROM Employees
WHERE name LIKE 'S%';
```
đĸ āĻāĻāĻŋ **S** āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§ āĻšāĻāĻ¯āĻŧāĻž āĻ¸āĻŦ āĻ¨āĻžāĻŽ āĻĻā§āĻāĻžāĻŦā§ (āĻ¯ā§āĻŽāĻ¨: **Samiul, Shamima, Shakila** āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)āĨ¤
---
### **ā§¨ī¸âŖ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ
āĻā§āĻˇāĻ° āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻˇ āĻšāĻāĻ¯āĻŧāĻž āĻĄāĻžāĻāĻž āĻā§āĻāĻāĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽ 'n' āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻˇ āĻšāĻ¯āĻŧā§āĻā§**
```sql
SELECT * FROM Employees
WHERE name LIKE '%n';
```
đĸ āĻāĻāĻŋ **n** āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻˇ āĻšāĻāĻ¯āĻŧāĻž āĻ¸āĻŦ āĻ¨āĻžāĻŽ āĻĻā§āĻāĻžāĻŦā§ (āĻ¯ā§āĻŽāĻ¨: **Jahan, Fahim, Rakibul** āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)āĨ¤
---
### **ā§Šī¸âŖ āĻ¨āĻžāĻŽā§āĻ° āĻŽāĻžāĻāĻāĻžāĻ¨ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ° āĻĨāĻžāĻāĻ˛ā§ āĻā§āĻāĻāĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽā§āĻ° āĻŽāĻžāĻā§ 'ah' āĻāĻā§**
```sql
SELECT * FROM Employees
WHERE name LIKE '%ah%';
```
đĸ āĻāĻāĻŋ āĻāĻŽāĻ¨ āĻ¨āĻžāĻŽ āĻĻā§āĻāĻžāĻŦā§ **āĻ¯ā§āĻā§āĻ˛ā§āĻ° āĻŽāĻžāĻā§ 'ah' āĻāĻā§** (āĻ¯ā§āĻŽāĻ¨: **Shamima, Mahmud, Fahim** āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)āĨ¤
---
## **đš `_` Wildcard āĻĻāĻŋāĻ¯āĻŧā§ āĻāĻĻāĻžāĻšāĻ°āĻŖ**
### **ā§§ī¸âŖ āĻ āĻŋāĻ ā§§āĻāĻŋ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ° āĻ°āĻŋāĻĒā§āĻ˛ā§āĻ¸ āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽā§āĻ° āĻĻā§āĻŦāĻŋāĻ¤ā§āĻ¯āĻŧ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ° 'a'**
```sql
SELECT * FROM Employees
WHERE name LIKE '_a%';
```
đĸ āĻāĻāĻŋ āĻāĻŽāĻ¨ āĻ¨āĻžāĻŽ āĻĻā§āĻāĻžāĻŦā§ **āĻ¯ā§āĻā§āĻ˛ā§āĻ° āĻĻā§āĻŦāĻŋāĻ¤ā§āĻ¯āĻŧ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ° 'a'** (āĻ¯ā§āĻŽāĻ¨: **Karim, Fahim, Samiul** āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)āĨ¤
---
### **ā§¨ī¸âŖ āĻļā§āĻˇā§āĻ° āĻāĻ āĻā§āĻ¯āĻžāĻ°ā§āĻā§āĻāĻžāĻ° āĻĢāĻŋāĻā§āĻ¸āĻĄ āĻ°ā§āĻā§ āĻā§āĻāĻāĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽā§āĻ° āĻļā§āĻˇā§āĻ° āĻāĻā§ 'a' āĻāĻā§**
```sql
SELECT * FROM Employees
WHERE name LIKE '%a_';
```
đĸ āĻāĻāĻŋ āĻāĻŽāĻ¨ āĻ¨āĻžāĻŽ āĻĻā§āĻāĻžāĻŦā§ **āĻ¯ā§āĻā§āĻ˛ā§āĻ° āĻļā§āĻˇā§āĻ° āĻāĻā§ 'a' āĻāĻā§** (āĻ¯ā§āĻŽāĻ¨: **Ayesha, Sumaiya** āĻāĻ¤ā§āĻ¯āĻžāĻĻāĻŋ)āĨ¤
---
## **đš `NOT LIKE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž āĻāĻŽāĻ¨ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ **āĻ¯āĻžāĻĻā§āĻ° āĻ¨āĻžāĻŽ 'S' āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§ āĻšāĻ¯āĻŧāĻ¨āĻŋ**
```sql
SELECT * FROM Employees
WHERE name NOT LIKE 'S%';
```
đĸ āĻāĻāĻŋ **S āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§ āĻšāĻāĻ¯āĻŧāĻž āĻ¨āĻžāĻŽ āĻŦāĻžāĻĻ āĻĻāĻŋāĻ¯āĻŧā§ āĻŦāĻžāĻāĻŋ āĻ¸āĻŦ āĻĻā§āĻāĻžāĻŦā§**āĨ¤
---
## **â
`LIKE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ°ā§āĻ° āĻ¸ā§āĻŦāĻŋāĻ§āĻž**
â **Flexible search:** āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ
āĻā§āĻˇāĻ° āĻĻāĻŋāĻ¯āĻŧā§ āĻļā§āĻ°ā§, āĻļā§āĻˇ āĻŦāĻž āĻŽāĻžāĻā§ āĻāĻŋāĻā§ āĻĨāĻžāĻāĻ˛ā§ āĻā§āĻāĻāĻ¤ā§ āĻĒāĻžāĻ°ā§
â **Wildcards:** `%` āĻāĻŦāĻ `_` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻāĻžāĻ¸ā§āĻāĻŽ āĻĒā§āĻ¯āĻžāĻāĻžāĻ°ā§āĻ¨ āĻŽāĻŋāĻ˛āĻžāĻ¨ā§ āĻ¯āĻžāĻ¯āĻŧ
â **Text filtering:** āĻ¨āĻžāĻŽ, āĻ āĻŋāĻāĻžāĻ¨āĻž āĻŦāĻž āĻ
āĻ¨ā§āĻ¯ āĻ¸ā§āĻā§āĻ°āĻŋāĻ āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ āĻā§āĻŦāĻ āĻĻāĻ°āĻāĻžāĻ°āĻŋ
---
### **`AND`, `OR`, āĻāĻŦāĻ `NOT` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `AND`, `OR`, āĻāĻŦāĻ `NOT` **āĻ˛āĻāĻŋāĻā§āĻ¯āĻžāĻ˛ āĻ
āĻĒāĻžāĻ°ā§āĻāĻ°** āĻšāĻŋāĻ¸āĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§ āĻāĻŦāĻ `WHERE` āĻā§āĻ˛āĻā§āĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§ **āĻŦāĻŋāĻāĻŋāĻ¨ā§āĻ¨ āĻāĻ¨ā§āĻĄāĻŋāĻļāĻ¨ āĻā§āĻ āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯**āĨ¤
---
## **â
ā§§. `AND` āĻ
āĻĒāĻžāĻ°ā§āĻāĻ° (āĻĻā§āĻāĻŋ āĻļāĻ°ā§āĻ¤ āĻāĻāĻ¸āĻžāĻĨā§ āĻĒā§āĻ°āĻŖ āĻāĻ°āĻ¤ā§ āĻšāĻŦā§)**
- `AND` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ **āĻ¸āĻŦ āĻļāĻ°ā§āĻ¤ āĻāĻāĻ¸āĻžāĻĨā§ āĻŽāĻŋāĻ˛ā§ āĻā§āĻ˛ā§ āĻ¤āĻŦā§āĻ āĻĄāĻžāĻāĻž āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§**āĨ¤
- āĻ
āĻ°ā§āĻĨāĻžā§, **āĻāĻā§ āĻļāĻ°ā§āĻ¤āĻ āĻ¸āĻ¤ā§āĻ¯ āĻšāĻ¤ā§ āĻšāĻŦā§**āĨ¤
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻžāĻ āĻāĻ°āĻž āĻāĻŦāĻ ā§Šā§Ļ āĻŦāĻāĻ° āĻŦāĻž āĻ¤āĻžāĻ° āĻŦā§āĻļāĻŋ āĻŦā§āĻ¸ā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE department = 'IT'
AND age >= 30;
```
đš **Result:** `department = 'IT'` āĻāĻŦāĻ `age >= 30`â**āĻāĻā§ āĻļāĻ°ā§āĻ¤ āĻŽāĻŋāĻ˛āĻ˛ā§** āĻ¤āĻŦā§āĻ āĻ°ā§ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§āĨ¤
---
## **â
ā§¨. `OR` āĻ
āĻĒāĻžāĻ°ā§āĻāĻ° (āĻāĻāĻāĻŋ āĻļāĻ°ā§āĻ¤ āĻŽāĻŋāĻ˛āĻ˛ā§āĻ āĻšāĻŦā§)**
- `OR` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻāĻāĻāĻŋ āĻļāĻ°ā§āĻ¤ āĻŽāĻŋāĻ˛āĻ˛ā§āĻ** āĻĄāĻžāĻāĻž āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§āĨ¤
- āĻ
āĻ°ā§āĻĨāĻžā§, **āĻ¯ā§ āĻā§āĻ¨ā§ āĻāĻāĻāĻŋāĻ āĻ¸āĻ¤ā§āĻ¯ āĻšāĻ¤ā§ āĻšāĻŦā§**āĨ¤
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž HR āĻŦāĻž IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻžāĻ āĻāĻ°ā§ āĻ¤āĻžāĻĻā§āĻ° āĻā§āĻāĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE department = 'HR'
OR department = 'IT';
```
đš **Result:** `HR` **āĻ
āĻĨāĻŦāĻž** `IT` āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¯ā§āĻā§āĻ¨ā§ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
## **â
ā§Š. `NOT` āĻ
āĻĒāĻžāĻ°ā§āĻāĻ° (āĻļāĻ°ā§āĻ¤ āĻ¨āĻž āĻŽāĻŋāĻ˛āĻ˛ā§ āĻ°āĻŋāĻāĻžāĻ°ā§āĻ¨ āĻāĻ°āĻŦā§)**
- `NOT` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§ **āĻļāĻ°ā§āĻ¤ā§āĻ° āĻāĻ˛ā§āĻā§ āĻŽāĻžāĻ¨ āĻŦā§āĻ° āĻāĻ°ā§**āĨ¤
- āĻ
āĻ°ā§āĻĨāĻžā§, **āĻ¯ā§ āĻļāĻ°ā§āĻ¤ āĻ¸āĻ¤ā§āĻ¯, āĻ¸ā§āĻāĻžāĻā§ āĻŽāĻŋāĻĨā§āĻ¯āĻž āĻŦāĻžāĻ¨āĻŋā§ā§ āĻĢā§āĻ˛ā§**āĨ¤
### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻ¨ā§āĻ, āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE NOT department = 'IT';
```
đš **Result:** `IT` āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ **āĻŦāĻžāĻāĻŋ āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**āĨ¤
---
## **â
`AND`, `OR`, āĻāĻŦāĻ `NOT` āĻāĻāĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž**
āĻāĻŽāĻ°āĻž āĻāĻžāĻ āĻ¯ā§ **āĻ¯āĻžāĻ°āĻž IT āĻŦāĻž Finance āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻžāĻ āĻāĻ°ā§ āĻāĻŦāĻ āĻ¯āĻžāĻĻā§āĻ° āĻŦā§āĻ¸ ā§¨ā§Ģ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ, āĻ¤āĻžāĻ°āĻž āĻ¯ā§āĻ¨ āĻĻā§āĻāĻžāĻ¨ā§ āĻšā§**:
```sql
SELECT * FROM Employees
WHERE (department = 'IT' OR department = 'Finance')
AND age > 25;
```
đš **Result:**
- `department = 'IT'` **āĻ
āĻĨāĻŦāĻž** `department = 'Finance'` â **āĻ¯ā§āĻā§āĻ¨ā§ āĻāĻāĻāĻŋ āĻšāĻ¤ā§ āĻšāĻŦā§**
- **āĻāĻŦāĻ** `age > 25` â **āĻŦā§āĻ¸ ā§¨ā§Ģ-āĻāĻ° āĻŦā§āĻļāĻŋ āĻšāĻ¤ā§ āĻšāĻŦā§**
---
## **â
`NOT` āĻ¸āĻš `AND` āĻāĻŦāĻ `OR` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž HR āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻ¨ā§āĻ āĻāĻŦāĻ āĻ¯āĻžāĻĻā§āĻ° āĻŦā§āĻ¸ ā§Šā§Ļ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ, āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE NOT department = 'HR'
AND age > 30;
```
đš **Result:**
- **HR āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻŦāĻžāĻĻ āĻ¯āĻžāĻŦā§**
- **āĻ¯āĻžāĻĻā§āĻ° āĻŦā§āĻ¸ ā§Šā§Ļ āĻŦāĻāĻ°ā§āĻ° āĻŦā§āĻļāĻŋ āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**
---
## **â
āĻ¸āĻāĻā§āĻˇā§āĻĒā§ āĻĒāĻžāĻ°ā§āĻĨāĻā§āĻ¯:**
| āĻ
āĻĒāĻžāĻ°ā§āĻāĻ° | āĻāĻžāĻ |
|----------|------------------------------------------------|
| `AND` | **āĻ¸āĻŦ āĻļāĻ°ā§āĻ¤ āĻ¸āĻ¤ā§āĻ¯ āĻšāĻ¤ā§ āĻšāĻŦā§** (āĻĻā§āĻāĻŋ āĻļāĻ°ā§āĻ¤āĻ āĻŽāĻŋāĻ˛āĻ¤ā§ āĻšāĻŦā§) |
| `OR` | **āĻ¯ā§āĻā§āĻ¨ā§ āĻāĻ āĻļāĻ°ā§āĻ¤ āĻ¸āĻ¤ā§āĻ¯ āĻšāĻ˛ā§āĻ āĻšāĻŦā§** |
| `NOT` | **āĻļāĻ°ā§āĻ¤ā§āĻ° āĻāĻ˛ā§āĻā§ āĻŽāĻžāĻ¨ āĻŦā§āĻ° āĻāĻ°ā§** |
---
### **`ORDER BY` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ `ORDER BY` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§ **āĻĄāĻžāĻāĻž āĻ¸āĻžāĻāĻžāĻ¨ā§āĻ° āĻāĻ¨ā§āĻ¯**āĨ¤ āĻāĻāĻŋ **āĻŦā§ āĻĨā§āĻā§ āĻā§āĻ āĻŦāĻž āĻā§āĻ āĻĨā§āĻā§ āĻŦā§ āĻā§āĻ°āĻŽā§ āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻĒāĻžāĻ°ā§**āĨ¤
---
## **â
`ORDER BY` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻāĻ āĻ¨ (Syntax)**
```sql
SELECT column_name FROM table_name
ORDER BY column_name [ASC | DESC];
```
đš `ASC` (Ascending) â **āĻā§āĻ āĻĨā§āĻā§ āĻŦā§** (default)
đš `DESC` (Descending) â **āĻŦā§ āĻĨā§āĻā§ āĻā§āĻ**
---
## **â
ā§§. `ORDER BY` āĻĻāĻŋā§ā§ āĻ¨āĻžāĻŽ āĻā§āĻ°āĻŽāĻžāĻ¨ā§āĻ¸āĻžāĻ°ā§ āĻ¸āĻžāĻāĻžāĻ¨ā§**
āĻ§āĻ°āĻŋ, āĻāĻŽāĻ°āĻž **āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ¨āĻžāĻŽ āĻŦāĻ°ā§āĻŖāĻžāĻ¨ā§āĻā§āĻ°āĻŽāĻŋāĻ (A-Z) āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
ORDER BY name;
```
āĻāĻāĻŋ **`name` āĻāĻ˛āĻžāĻŽā§āĻ° āĻŽāĻžāĻ¨ A āĻĨā§āĻā§ Z āĻĒāĻ°ā§āĻ¯āĻ¨ā§āĻ¤ āĻ¸āĻžāĻāĻžāĻŦā§**āĨ¤
---
## **â
ā§¨. `ORDER BY` āĻĻāĻŋā§ā§ āĻŦā§āĻ¤āĻ¨ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¸āĻžāĻāĻžāĻ¨ā§ (Ascending & Descending)**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ (salary) āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻā§āĻ āĻĨā§āĻā§ āĻŦā§ (Ascending)** āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻāĻžāĻ:
```sql
SELECT * FROM Employees
ORDER BY salary ASC;
```
đĸ āĻāĻāĻŋ **āĻ¸āĻŦāĻā§ā§ā§ āĻāĻŽ āĻŦā§āĻ¤āĻ¨ āĻĨā§āĻā§ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¤āĻ¨ā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**āĨ¤
đš **āĻŦā§ āĻĨā§āĻā§ āĻā§āĻ (Descending) āĻ¸āĻžāĻāĻžāĻ¤ā§:**
```sql
SELECT * FROM Employees
ORDER BY salary DESC;
```
đĸ āĻāĻāĻŋ **āĻ¸āĻŦāĻā§ā§ā§ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¤āĻ¨ āĻĒāĻžāĻā§āĻž āĻāĻ°ā§āĻŽā§āĻā§ āĻ¸āĻŦāĻžāĻ° āĻāĻĒāĻ°ā§ āĻĻā§āĻāĻžāĻŦā§**āĨ¤
---
## **â
ā§Š. āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§āĻ° āĻāĻĒāĻ° `ORDER BY`**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻāĻžāĻ āĻāĻŦāĻ āĻāĻāĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻā§āĻ¤āĻ°ā§ āĻŦā§āĻ¸ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ (Ascending) āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
ORDER BY department ASC, age ASC;
```
đš āĻāĻāĻŋ **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¸āĻžāĻāĻžāĻŦā§ āĻāĻŦāĻ āĻāĻāĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻŽāĻ§ā§āĻ¯ā§ āĻŦā§āĻ¸ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¸āĻžāĻāĻžāĻŦā§**āĨ¤
---
## **â
ā§Ē. `ORDER BY` `WHERE` āĻāĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž**
āĻ¯āĻĻāĻŋ āĻāĻŽāĻ°āĻž **āĻ¯āĻžāĻ°āĻž IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻāĻžāĻ āĻāĻ°ā§, āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻāĻžāĻ**:
```sql
SELECT * FROM Employees
WHERE department = 'IT'
ORDER BY salary DESC;
```
đš āĻāĻāĻŋ **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° IT āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§ āĻāĻŦāĻ āĻ¤āĻžāĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻŦā§ āĻĨā§āĻā§ āĻā§āĻ āĻ¸āĻžāĻāĻžāĻŦā§**āĨ¤
---
## **â
āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `ORDER BY` āĻāĻ° āĻ¸ā§āĻŦāĻŋāĻ§āĻž**
â **āĻĄāĻžāĻāĻž āĻ¸āĻžāĻāĻžāĻ¨ā§ āĻ¸āĻšāĻ āĻšā§**
â **Ascending āĻŦāĻž Descending āĻ¯ā§āĻā§āĻ¨ā§āĻāĻžāĻŦā§ āĻ¸āĻžāĻāĻžāĻ¨ā§ āĻ¯āĻžā§**
â **āĻŦā§ āĻĄāĻžāĻāĻžāĻŦā§āĻā§ āĻ°āĻŋāĻĒā§āĻ°ā§āĻ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ āĻā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§āĻ°ā§āĻŖ**
---
### **`NULL` āĻāĻŦāĻ `NOT NULL` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ **`NULL`** āĻŽāĻžāĻ¨ā§ āĻšāĻ˛ā§ **āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻ¨ā§āĻ āĻŦāĻž āĻ
āĻāĻžāĻ¨āĻž āĻŽāĻžāĻ¨**, āĻāĻ° **`NOT NULL`** āĻŽāĻžāĻ¨ā§ āĻšāĻ˛ā§ **āĻ āĻāĻ˛āĻžāĻŽā§ āĻ
āĻŦāĻļā§āĻ¯āĻ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻ¤ā§ āĻšāĻŦā§**āĨ¤
---
## **â
`NULL` āĻ `NOT NULL` āĻāĻ° āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ āĻŦā§āĻ¯āĻžāĻā§āĻ¯āĻž**
- **`NULL`** â āĻ¯āĻĻāĻŋ āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§ **āĻŽāĻžāĻ¨ āĻ¨āĻž āĻĨāĻžāĻā§**, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¸ā§āĻāĻŋ `NULL` āĻšāĻŦā§āĨ¤
- **`NOT NULL`** â āĻ¯āĻĻāĻŋ āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§ `NOT NULL` āĻĻā§ā§āĻž āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ **āĻ¸ā§āĻ āĻāĻ˛āĻžāĻŽā§ āĻ
āĻŦāĻļā§āĻ¯āĻ āĻĄāĻžāĻāĻž āĻĻāĻŋāĻ¤ā§ āĻšāĻŦā§**āĨ¤
---
## **â
`NULL` āĻ `NOT NULL` āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋāĻ¤ā§ āĻāĻŋāĻāĻžāĻŦā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§?**
```sql
CREATE TABLE employees (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL, -- āĻāĻāĻžāĻ¨ā§ āĻ
āĻŦāĻļā§āĻ¯āĻ āĻ¨āĻžāĻŽ āĻĻāĻŋāĻ¤ā§ āĻšāĻŦā§
department VARCHAR(30) NULL, -- āĻāĻāĻžāĻ¨ā§ āĻĄāĻžāĻāĻž āĻ¨āĻž āĻĻāĻŋāĻ˛ā§āĻ āĻšāĻŦā§
age INT CHECK (age >= 18),
salary DECIMAL(10,2) NOT NULL, -- āĻ
āĻŦāĻļā§āĻ¯āĻ āĻŦā§āĻ¤āĻ¨ āĻĻāĻŋāĻ¤ā§ āĻšāĻŦā§
join_date DATE NULL -- āĻ¤āĻžāĻ°āĻŋāĻ āĻĻā§āĻā§āĻž āĻŦāĻžāĻ§ā§āĻ¯āĻ¤āĻžāĻŽā§āĻ˛āĻ āĻ¨āĻž
);
```
đš **`NOT NULL` āĻĨāĻžāĻāĻž āĻŽāĻžāĻ¨ā§** â āĻ āĻāĻ˛āĻžāĻŽā§ āĻĄāĻžāĻāĻž **āĻ
āĻŦāĻļā§āĻ¯āĻ āĻĻāĻŋāĻ¤ā§ āĻšāĻŦā§**āĨ¤
đš **`NULL` āĻĨāĻžāĻāĻž āĻŽāĻžāĻ¨ā§** â āĻ āĻāĻ˛āĻžāĻŽā§ āĻĄāĻžāĻāĻž **āĻ¨āĻž āĻĻāĻŋāĻ˛ā§āĻ āĻāĻ˛āĻŦā§**āĨ¤
---
## **â
`NULL` āĻĄāĻžāĻāĻž āĻāĻ¨āĻ¸āĻžāĻ°ā§āĻ āĻāĻ°āĻž**
```sql
INSERT INTO employees (name, department, age, salary, join_date)
VALUES ('Samiul', NULL, 25, 50000.00, '2022-03-15');
```
đš āĻāĻāĻžāĻ¨ā§ **`department` āĻāĻ˛āĻžāĻŽā§ `NULL` āĻ°āĻžāĻāĻž āĻšā§ā§āĻā§**āĨ¤
---
## **â
`NOT NULL` āĻāĻ˛āĻžāĻŽā§ `NULL` āĻĻāĻŋāĻ˛ā§ āĻā§ āĻšāĻŦā§?**
```sql
INSERT INTO employees (name, department, age, salary, join_date)
VALUES (NULL, 'IT', 25, 50000.00, '2022-03-15');
```
â **Error: Column 'name' cannot be null**
đš āĻāĻžāĻ°āĻŖ **`name` āĻāĻ˛āĻžāĻŽā§ `NOT NULL` āĻĻā§ā§āĻž āĻāĻā§**, āĻ¤āĻžāĻ `NULL` āĻĻā§āĻā§āĻž āĻ¯āĻžāĻŦā§ āĻ¨āĻžāĨ¤
---
## **â
`NULL` āĻā§āĻ āĻāĻ°āĻž (WHERE āĻ¸āĻš)**
đš **`IS NULL` āĻĻāĻŋā§ā§ āĻā§āĻ āĻāĻ°āĻž āĻšā§ āĻā§āĻ¨ āĻāĻ˛āĻžāĻŽ `NULL` āĻāĻā§ āĻāĻŋāĻ¨āĻž**
```sql
SELECT * FROM employees WHERE department IS NULL;
```
đš **āĻ¯ā§āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§āĻ° `department` `NULL`, āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**
đš **`IS NOT NULL` āĻĻāĻŋā§ā§ `NULL` āĻ¨āĻž āĻĨāĻžāĻāĻž āĻĄāĻžāĻāĻž āĻā§āĻāĻāĻ¤ā§ āĻĒāĻžāĻ°āĻŋ**
```sql
SELECT * FROM employees WHERE department IS NOT NULL;
```
đš **āĻ¯āĻžāĻĻā§āĻ° `department` āĻ āĻŽāĻžāĻ¨ āĻāĻā§, āĻļā§āĻ§ā§ āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§**
---
## **â
`NULL` āĻĢāĻŋāĻ˛ā§āĻĄ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž (`UPDATE` āĻ¸āĻš)**
```sql
UPDATE employees
SET department = 'HR'
WHERE department IS NULL;
```
đš **āĻ¯āĻžāĻĻā§āĻ° `department` `NULL`, āĻ¤āĻžāĻĻā§āĻ° `HR` āĻ¸ā§āĻ āĻāĻ°āĻž āĻšāĻŦā§**
---
## **â
`NULL` āĻā§ `DEFAULT` āĻŽāĻžāĻ¨ āĻ¸ā§āĻ āĻāĻ°āĻž**
```sql
CREATE TABLE employees (
id INT PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(50) NOT NULL,
department VARCHAR(30) DEFAULT 'Unknown',
age INT CHECK (age >= 18),
salary DECIMAL(10,2) NOT NULL,
join_date DATE NULL
);
```
đš **āĻ¯āĻĻāĻŋ `department`-āĻ āĻā§āĻ¨ā§ āĻŽāĻžāĻ¨ āĻ¨āĻž āĻĻā§āĻā§āĻž āĻšā§, āĻ¤āĻžāĻšāĻ˛ā§ āĻ¸ā§āĻŦā§āĻāĻā§āĻ°āĻŋā§āĻāĻžāĻŦā§ 'Unknown' āĻšā§ā§ āĻ¯āĻžāĻŦā§**
---
### đĨ **āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `NULL` āĻāĻŦāĻ `NOT NULL`**
â **`NULL`** â āĻāĻ˛āĻžāĻŽā§ āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻ¨āĻž āĻĨāĻžāĻāĻ˛ā§ `NULL` āĻšāĻ¤ā§ āĻĒāĻžāĻ°ā§
â **`NOT NULL`** â āĻāĻ˛āĻžāĻŽā§ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻž āĻŦāĻžāĻ§ā§āĻ¯āĻ¤āĻžāĻŽā§āĻ˛āĻ
â **`IS NULL`** â `NULL` āĻā§āĻ āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯
â **`IS NOT NULL`** â `NULL` āĻ¨āĻž āĻĨāĻžāĻāĻž āĻā§āĻ āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯
â **`UPDATE` āĻĻāĻŋā§ā§ `NULL` āĻĢāĻŋāĻ˛ā§āĻĄ āĻāĻĒāĻĄā§āĻ āĻāĻ°āĻž āĻ¯āĻžā§**
---
### **đš `ON` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§? (āĻĒā§āĻ°ā§āĻŖāĻžāĻā§āĻ āĻāĻĻāĻžāĻšāĻ°āĻŖ)**
āĻāĻŽāĻ°āĻž āĻĻā§āĻāĻŋ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§:
1. **`employees`** â āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĨāĻžāĻāĻŦā§
2. **`departments`** â āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĨāĻžāĻāĻŦā§
āĻāĻ°āĻĒāĻ° āĻāĻŽāĻ°āĻž **`ON` āĻ¸āĻš `JOIN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§** āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ¸āĻžāĻĨā§ āĻ¤āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻŽāĻŋāĻ˛āĻŋā§ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **â
`CREATE TABLE` - āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻž**
```sql
CREATE TABLE departments (
id INT PRIMARY KEY,
department_name VARCHAR(50) NOT NULL
);
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(50) NOT NULL,
department_id INT,
FOREIGN KEY (department_id) REFERENCES departments(id)
);
```
đš **`departments` āĻā§āĻŦāĻŋāĻ˛ā§ āĻĒā§āĻ°āĻ¤āĻŋāĻāĻŋ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¨āĻžāĻŽ āĻĨāĻžāĻāĻŦā§āĨ¤**
đš **`employees` āĻā§āĻŦāĻŋāĻ˛ā§ `department_id` āĻĢāĻŋāĻ˛ā§āĻĄ āĻāĻā§**, āĻ¯āĻž `departments` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `id` āĻāĻ° āĻ¸āĻžāĻĨā§ āĻ¸āĻŽā§āĻĒāĻ°ā§āĻāĻŋāĻ¤āĨ¤
---
### **â
`INSERT INTO` - āĻĄāĻžāĻāĻž āĻ¯ā§āĻ āĻāĻ°āĻž**
```sql
INSERT INTO departments (id, department_name) VALUES
(101, 'IT'),
(102, 'HR'),
(103, 'Marketing');
INSERT INTO employees (id, name, department_id) VALUES
(1, 'Arafat', 101),
(2, 'Samiul', 102),
(3, 'Shuvo', 103),
(4, 'Alex', NULL);
```
đš **`departments` āĻā§āĻŦāĻŋāĻ˛ā§ ā§ŠāĻāĻŋ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¯ā§āĻ āĻāĻ°āĻž āĻšāĻ˛ā§āĨ¤**
đš **`employees` āĻā§āĻŦāĻŋāĻ˛ā§ ā§Ē āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻ¯ā§āĻ āĻāĻ°āĻž āĻšāĻ˛ā§āĨ¤**
đš **Alex-āĻāĻ° `department_id` `NULL`, āĻŽāĻžāĻ¨ā§ āĻ¸ā§ āĻā§āĻ¨ā§ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻ¨ā§āĻāĨ¤**
---
### **â
`ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ `INNER JOIN`**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;
```
đš **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻāĻā§, āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§āĨ¤**
#### **đ Output:**
| name | department_name |
|--------|---------------|
| Arafat | IT |
| Samiul | HR |
| Shuvo | Marketing |
đš **Alex āĻ¨ā§āĻ, āĻāĻžāĻ°āĻŖ āĻ¤āĻžāĻ° `department_id` `NULL`āĨ¤**
---
### **â
`ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ `LEFT JOIN`**
```sql
SELECT employees.name, departments.department_name
FROM employees
LEFT JOIN departments
ON employees.department_id = departments.id;
```
đš **āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžāĻŦā§, āĻāĻŽāĻ¨āĻāĻŋ āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ āĻ¤āĻžāĻĻā§āĻ°āĻāĨ¤**
#### **đ Output:**
| name | department_name |
|--------|---------------|
| Arafat | IT |
| Samiul | HR |
| Shuvo | Marketing |
| Alex | NULL |
đš **Alex-āĻāĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ, āĻ¤āĻžāĻ `NULL` āĻĻā§āĻāĻžāĻŦā§āĨ¤**
---
### **â
`ON` āĻāĻŦāĻ `USING` āĻāĻ° āĻĒāĻžāĻ°ā§āĻĨāĻā§āĻ¯**
đš **āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻ˛āĻžāĻĻāĻž āĻšā§, āĻ¤āĻžāĻšāĻ˛ā§ `ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻšā§āĨ¤**
đš **āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻāĻ āĻ¨āĻžāĻŽā§āĻ° āĻāĻ˛āĻžāĻŽ āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ `USING` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§āĨ¤**
#### **`ON` āĻĻāĻŋā§ā§ JOIN (āĻ¯ā§āĻšā§āĻ¤ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻŋāĻ¨ā§āĻ¨)**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;
```
#### **`USING` āĻĻāĻŋā§ā§ JOIN (āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ `department_id` āĻĨāĻžāĻā§)**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
USING (department_id);
```
---
### đĨ **āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `ON`**
â **`ON` āĻŽā§āĻ˛āĻ¤ `JOIN` āĻāĻ° āĻā§āĻˇā§āĻ¤ā§āĻ°ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻšā§āĨ¤**
â **`ON` āĻ¯āĻāĻ¨ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻšā§?** â āĻ¯āĻāĻ¨ āĻĻā§āĻ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŽā§āĻĒāĻ°ā§āĻāĻŋāĻ¤ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻŋāĻ¨ā§āĻ¨ āĻšā§āĨ¤
â **`INNER JOIN`** â āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¯āĻžāĻĻā§āĻ° āĻŽāĻŋāĻ˛ āĻĒāĻžāĻā§āĻž āĻ¯āĻžā§, āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžā§āĨ¤
â **`LEFT JOIN`** â āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžā§, āĻāĻŽāĻ¨āĻāĻŋ āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ, āĻ¤āĻžāĻĻā§āĻ°āĻāĨ¤
â **`USING` āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§, āĻ¯āĻāĻ¨ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻāĻ āĻšā§āĨ¤**
---
### **đš `ON` āĻāĻŋāĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§? (āĻĒā§āĻ°ā§āĻŖāĻžāĻā§āĻ āĻāĻĻāĻžāĻšāĻ°āĻŖ)**
āĻāĻŽāĻ°āĻž āĻĻā§āĻāĻŋ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻŦā§:
1. **`employees`** â āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĨāĻžāĻāĻŦā§
2. **`departments`** â āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¤āĻĨā§āĻ¯ āĻĨāĻžāĻāĻŦā§
āĻāĻ°āĻĒāĻ° āĻāĻŽāĻ°āĻž **`ON` āĻ¸āĻš `JOIN` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§** āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻ¸āĻžāĻĨā§ āĻ¤āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻŽāĻŋāĻ˛āĻŋā§ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **â
`CREATE TABLE` - āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻž**
```sql
CREATE TABLE departments (
id INT PRIMARY KEY,
department_name VARCHAR(50) NOT NULL
);
CREATE TABLE employees (
id INT PRIMARY KEY,
name VARCHAR(50) NOT NULL,
department_id INT,
FOREIGN KEY (department_id) REFERENCES departments(id)
);
```
đš **`departments` āĻā§āĻŦāĻŋāĻ˛ā§ āĻĒā§āĻ°āĻ¤āĻŋāĻāĻŋ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¨āĻžāĻŽ āĻĨāĻžāĻāĻŦā§āĨ¤**
đš **`employees` āĻā§āĻŦāĻŋāĻ˛ā§ `department_id` āĻĢāĻŋāĻ˛ā§āĻĄ āĻāĻā§**, āĻ¯āĻž `departments` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `id` āĻāĻ° āĻ¸āĻžāĻĨā§ āĻ¸āĻŽā§āĻĒāĻ°ā§āĻāĻŋāĻ¤āĨ¤
---
### **â
`INSERT INTO` - āĻĄāĻžāĻāĻž āĻ¯ā§āĻ āĻāĻ°āĻž**
```sql
INSERT INTO departments (id, department_name) VALUES
(101, 'IT'),
(102, 'HR'),
(103, 'Marketing');
INSERT INTO employees (id, name, department_id) VALUES
(1, 'Arafat', 101),
(2, 'Samiul', 102),
(3, 'Shuvo', 103),
(4, 'Alex', NULL);
```
đš **`departments` āĻā§āĻŦāĻŋāĻ˛ā§ ā§ŠāĻāĻŋ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¯ā§āĻ āĻāĻ°āĻž āĻšāĻ˛ā§āĨ¤**
đš **`employees` āĻā§āĻŦāĻŋāĻ˛ā§ ā§Ē āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻ¯ā§āĻ āĻāĻ°āĻž āĻšāĻ˛ā§āĨ¤**
đš **Alex-āĻāĻ° `department_id` `NULL`, āĻŽāĻžāĻ¨ā§ āĻ¸ā§ āĻā§āĻ¨ā§ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§ āĻ¨ā§āĻāĨ¤**
---
### **â
`ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ `INNER JOIN`**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;
```
đš **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻāĻā§, āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžāĻŦā§āĨ¤**
#### **đ Output:**
| name | department_name |
|--------|---------------|
| Arafat | IT |
| Samiul | HR |
| Shuvo | Marketing |
đš **Alex āĻ¨ā§āĻ, āĻāĻžāĻ°āĻŖ āĻ¤āĻžāĻ° `department_id` `NULL`āĨ¤**
---
### **â
`ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ `LEFT JOIN`**
```sql
SELECT employees.name, departments.department_name
FROM employees
LEFT JOIN departments
ON employees.department_id = departments.id;
```
đš **āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžāĻŦā§, āĻāĻŽāĻ¨āĻāĻŋ āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ āĻ¤āĻžāĻĻā§āĻ°āĻāĨ¤**
#### **đ Output:**
| name | department_name |
|--------|---------------|
| Arafat | IT |
| Samiul | HR |
| Shuvo | Marketing |
| Alex | NULL |
đš **Alex-āĻāĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ, āĻ¤āĻžāĻ `NULL` āĻĻā§āĻāĻžāĻŦā§āĨ¤**
---
### **â
`ON` āĻāĻŦāĻ `USING` āĻāĻ° āĻĒāĻžāĻ°ā§āĻĨāĻā§āĻ¯**
đš **āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻ˛āĻžāĻĻāĻž āĻšā§, āĻ¤āĻžāĻšāĻ˛ā§ `ON` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻšā§āĨ¤**
đš **āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻāĻ āĻ¨āĻžāĻŽā§āĻ° āĻāĻ˛āĻžāĻŽ āĻĨāĻžāĻā§, āĻ¤āĻžāĻšāĻ˛ā§ `USING` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§āĨ¤**
#### **`ON` āĻĻāĻŋā§ā§ JOIN (āĻ¯ā§āĻšā§āĻ¤ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻŋāĻ¨ā§āĻ¨)**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
ON employees.department_id = departments.id;
```
#### **`USING` āĻĻāĻŋā§ā§ JOIN (āĻ¯āĻĻāĻŋ āĻāĻā§ āĻā§āĻŦāĻŋāĻ˛ā§ `department_id` āĻĨāĻžāĻā§)**
```sql
SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments
USING (department_id);
```
---
### đĨ **āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `ON`**
â **`ON` āĻŽā§āĻ˛āĻ¤ `JOIN` āĻāĻ° āĻā§āĻˇā§āĻ¤ā§āĻ°ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻšā§āĨ¤**
â **`ON` āĻ¯āĻāĻ¨ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻšā§?** â āĻ¯āĻāĻ¨ āĻĻā§āĻ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŽā§āĻĒāĻ°ā§āĻāĻŋāĻ¤ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻŋāĻ¨ā§āĻ¨ āĻšā§āĨ¤
â **`INNER JOIN`** â āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¯āĻžāĻĻā§āĻ° āĻŽāĻŋāĻ˛ āĻĒāĻžāĻā§āĻž āĻ¯āĻžā§, āĻ¤āĻžāĻĻā§āĻ° āĻĻā§āĻāĻžā§āĨ¤
â **`LEFT JOIN`** â āĻ¸āĻŦ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžā§, āĻāĻŽāĻ¨āĻāĻŋ āĻ¯āĻžāĻĻā§āĻ° āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨ā§āĻ, āĻ¤āĻžāĻĻā§āĻ°āĻāĨ¤
â **`USING` āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§, āĻ¯āĻāĻ¨ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¨āĻžāĻŽ āĻāĻāĻ āĻšā§āĨ¤**
---
### **đš SQL-āĻ `DUPLICATE TABLE` āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻžāĻ° āĻāĻĒāĻžā§**
đš **āĻā§āĻ¨ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻ āĻĄāĻžāĻāĻž āĻā§āĻ˛ā§āĻ¨ (Copy) āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ `CREATE TABLE ... AS` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§āĨ¤**
đš **āĻā§āĻ¨ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻā§āĻ˛ā§āĻ¨ āĻāĻ°āĻ¤ā§ `CREATE TABLE ... LIKE` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§āĨ¤**
---
## **â
ā§§. āĻ¸āĻŽā§āĻĒā§āĻ°ā§āĻŖ āĻā§āĻŦāĻŋāĻ˛ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻāĻ°āĻž (`CREATE TABLE ... AS`)**
đš **āĻāĻāĻāĻŋ āĻŦāĻŋāĻĻā§āĻ¯āĻŽāĻžāĻ¨ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻāĻ˛ āĻĄāĻžāĻāĻž āĻ¸āĻš āĻ¨āĻ¤ā§āĻ¨ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻ¤ā§:**
```sql
CREATE TABLE employees_duplicate AS
SELECT * FROM employees;
```
đš **`employees_duplicate` āĻ¨āĻžāĻŽā§ āĻ¨āĻ¤ā§āĻ¨ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻšāĻŦā§, āĻ¯ā§āĻāĻžāĻ¨ā§ `employees` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŦ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻŦā§āĨ¤**
#### **đ Output (āĻ¨āĻ¤ā§āĻ¨ `employees_duplicate` āĻā§āĻŦāĻŋāĻ˛)**
| id | name | department | salary |
|----|------|-----------|--------|
| 1 | Arafat | IT | 50000 |
| 2 | Samiul | HR | 40000 |
| 3 | Shuvo | Marketing | 45000 |
---
## **â
ā§¨. āĻļā§āĻ§ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻāĻ°āĻž (`CREATE TABLE ... LIKE`)**
đš **āĻļā§āĻ§ā§ āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻā§āĻ˛ā§āĻ¨ āĻāĻ°āĻ¤ā§ āĻāĻžāĻāĻ˛ā§:**
```sql
CREATE TABLE employees_structure LIKE employees;
```
đš **āĻāĻ¤ā§ āĻļā§āĻ§ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻšāĻŦā§, āĻāĻŋāĻ¨ā§āĻ¤ā§ āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻŦā§ āĻ¨āĻžāĨ¤**
#### **đ Output (āĻ¨āĻ¤ā§āĻ¨ `employees_structure` āĻā§āĻŦāĻŋāĻ˛, āĻāĻŋāĻ¨ā§āĻ¤ā§ āĻāĻžāĻ˛āĻŋ)**
| id | name | department | salary |
|----|------|-----------|--------|
| | | | |
đš **āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻ¨ā§āĻ, āĻāĻžāĻ°āĻŖ `LIKE` āĻļā§āĻ§ā§ āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻāĻ°ā§, āĻĄāĻžāĻāĻž āĻ¨āĻžāĨ¤**
---
## **â
ā§Š. āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻāĻŋāĻā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻĄāĻžāĻāĻž āĻāĻĒāĻŋ āĻāĻ°āĻž**
đš **āĻ§āĻ°ā§āĻ¨, āĻļā§āĻ§ā§ `name` āĻāĻŦāĻ `salary` āĻĄāĻžāĻāĻž āĻ¸āĻš āĻ¨āĻ¤ā§āĻ¨ āĻā§āĻŦāĻŋāĻ˛ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻ¤ā§ āĻāĻžāĻ:**
```sql
CREATE TABLE high_salary_employees AS
SELECT name, salary FROM employees WHERE salary > 40000;
```
đš **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¯āĻžāĻĻā§āĻ° `salary > 40000` āĻ¤āĻžāĻ°āĻž `high_salary_employees` āĻā§āĻŦāĻŋāĻ˛ā§ āĻĨāĻžāĻāĻŦā§āĨ¤**
#### **đ Output (āĻ¨āĻ¤ā§āĻ¨ `high_salary_employees` āĻā§āĻŦāĻŋāĻ˛)**
| name | salary |
|--------|--------|
| Arafat | 50000 |
| Shuvo | 45000 |
---
## **â
ā§Ē. āĻā§āĻŦāĻŋāĻ˛ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻāĻ°āĻžāĻ° āĻĒāĻ°ā§ āĻ¨āĻ¤ā§āĻ¨ āĻĄāĻžāĻāĻž āĻ¯ā§āĻ āĻāĻ°āĻž**
```sql
INSERT INTO employees_duplicate (id, name, department, salary)
VALUES (4, 'Alex', 'Finance', 42000);
```
đš **āĻāĻ¤ā§ `employees_duplicate` āĻā§āĻŦāĻŋāĻ˛ā§ āĻ¨āĻ¤ā§āĻ¨ āĻ°ā§ āĻ¯ā§āĻ āĻšāĻŦā§, āĻāĻŋāĻ¨ā§āĻ¤ā§ `employees` āĻā§āĻŦāĻŋāĻ˛ āĻ
āĻā§āĻˇāĻ¤ āĻĨāĻžāĻāĻŦā§āĨ¤**
---
## đĨ **āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `DUPLICATE TABLE`**
â **`CREATE TABLE new_table AS SELECT * FROM old_table;`** â āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻ āĻĄāĻžāĻāĻž āĻāĻĒāĻŋ āĻāĻ°āĻŦā§āĨ¤
â **`CREATE TABLE new_table LIKE old_table;`** â āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻāĻ°āĻŦā§, āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻŦā§ āĻ¨āĻžāĨ¤
â **āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻāĻ˛āĻžāĻŽā§āĻ° āĻĄāĻžāĻāĻž āĻāĻĒāĻŋ āĻāĻ°āĻ¤ā§ `SELECT column1, column2 FROM table` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§āĨ¤**
---
### **đš `dummy_employee` āĻ¨āĻžāĻŽā§ `employees` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻ¤ā§āĻ°āĻŋ āĻāĻ°āĻž**
đš **āĻāĻĒāĻ¨āĻŋ `employees` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŦ āĻĄāĻžāĻāĻž āĻ āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°ā§āĻ¨ āĻ¨āĻŋāĻā§āĻ° āĻĻā§āĻāĻŋ āĻĒāĻĻā§āĻ§āĻ¤āĻŋāĻ¤ā§:**
---
### **â
`CREATE TABLE ... AS SELECT * FROM` (āĻĄāĻžāĻāĻž āĻ āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻāĻ°āĻŦā§)**
```sql
CREATE TABLE dummy_employee AS
SELECT * FROM employees;
```
đš **āĻāĻāĻŋ `employees` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŦ āĻāĻ˛āĻžāĻŽ āĻ āĻĄāĻžāĻāĻž `dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻĒāĻŋ āĻāĻ°āĻŦā§āĨ¤**
---
### **â
`CREATE TABLE ... LIKE` (āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ¸ā§āĻā§āĻ°āĻžāĻāĻāĻžāĻ° āĻāĻĒāĻŋ āĻāĻ°āĻŦā§, āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻŦā§ āĻ¨āĻž)**
```sql
CREATE TABLE dummy_employee LIKE employees;
```
đš **āĻāĻ¤ā§ `dummy_employee` āĻā§āĻŦāĻŋāĻ˛ `employees` āĻāĻ° āĻŽāĻ¤ā§āĻ āĻšāĻŦā§, āĻāĻŋāĻ¨ā§āĻ¤ā§ āĻā§āĻ¨ā§ āĻĄāĻžāĻāĻž āĻĨāĻžāĻāĻŦā§ āĻ¨āĻžāĨ¤**
đš **āĻĄāĻžāĻāĻž āĻ¯ā§āĻ āĻāĻ°āĻ¤ā§ āĻāĻžāĻāĻ˛ā§:**
```sql
INSERT INTO dummy_employee SELECT * FROM employees;
```
---
### **â
āĻ¨āĻŋāĻļā§āĻāĻŋāĻ¤ āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ `SELECT` āĻāĻ°ā§ āĻĻā§āĻā§āĻ¨:**
```sql
SELECT * FROM dummy_employee;
```
đš **āĻāĻ¤ā§ `dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻ¸āĻŦ āĻĄāĻžāĻāĻž āĻĻā§āĻāĻ¤ā§ āĻĒāĻžāĻŦā§āĻ¨āĨ¤**
---
### **đš `dummy_employee` āĻā§āĻŦāĻŋāĻ˛ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ `LIMIT` āĻŦā§āĻāĻŋā§ā§ āĻĻā§āĻā§āĻž**
āĻāĻāĻ¨ āĻĨā§āĻā§ **`dummy_employee`** āĻā§āĻŦāĻŋāĻ˛ āĻ¨āĻŋā§ā§ āĻāĻžāĻ āĻāĻ°āĻŦā§ āĻāĻŦāĻ `LIMIT` āĻ¸āĻŽā§āĻĒāĻ°ā§āĻā§ āĻŦāĻŋāĻ¸ā§āĻ¤āĻžāĻ°āĻŋāĻ¤ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
## **â
`LIMIT` āĻĻāĻŋā§ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻ¨ā§**
đš āĻĒā§āĻ°āĻĨāĻŽ **ā§Ģ āĻāĻ¨ āĻāĻ°ā§āĻŽā§** āĻĻā§āĻāĻžāĻ¤ā§ āĻāĻžāĻāĻ˛ā§:
```sql
SELECT * FROM dummy_employee
LIMIT 5;
```
đš **đ Output:**
| id | name | department | salary |
|----|------|-----------|--------|
| 1 | Arafat | IT | 50000 |
| 2 | Samiul | HR | 40000 |
| 3 | Shuvo | Marketing | 45000 |
| 4 | Alex | Finance | 42000 |
| 5 | John | IT | 46000 |
---
## **â
`LIMIT` + `ORDER BY` (āĻ¸āĻŦāĻā§ā§ā§ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¤āĻ¨ā§āĻ° ā§Š āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžāĻ¨ā§)**
```sql
SELECT * FROM dummy_employee
ORDER BY salary DESC
LIMIT 3;
```
đš **đ Output:**
| id | name | department | salary |
|----|------|-----------|--------|
| 1 | Arafat | IT | 50000 |
| 5 | John | IT | 46000 |
| 3 | Shuvo | Marketing | 45000 |
---
## **â
`LIMIT` + `OFFSET` (āĻĻā§āĻŦāĻŋāĻ¤ā§ā§ āĻĒā§āĻˇā§āĻ āĻžāĻ° āĻĄāĻžāĻāĻž āĻāĻ¨āĻ¤ā§)**
đš āĻĒā§āĻ°āĻĨāĻŽ **ā§ĢāĻāĻŋ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻĒāĻ°ā§āĻ° ā§ĢāĻāĻŋ āĻ°ā§ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĻ˛ā§:**
```sql
SELECT * FROM dummy_employee
LIMIT 5 OFFSET 5;
```
đš **đ Output:**
| id | name | department | salary |
|----|------|-----------|--------|
| 6 | Michael | HR | 39000 |
| 7 | Sarah | IT | 42000 |
| 8 | David | Finance | 41000 |
| 9 | Emma | HR | 43000 |
| 10 | James | IT | 40000 |
---
## **â
`LIMIT` + `WHERE` (āĻļāĻ°ā§āĻ¤ āĻĻāĻŋā§ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻ¨ā§)**
đš **āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° `IT` āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻĒā§āĻ°āĻĨāĻŽ ā§¨ āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĻ˛ā§:**
```sql
SELECT * FROM dummy_employee
WHERE department = 'IT'
LIMIT 2;
```
đš **đ Output:**
| id | name | department | salary |
|----|------|-----------|--------|
| 1 | Arafat | IT | 50000 |
| 5 | John | IT | 46000 |
---
## **â
`LIMIT` + `DELETE` (āĻļā§āĻ§ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻŽā§āĻāĻ¤ā§)**
đš āĻ¯āĻĻāĻŋ **āĻļā§āĻ§ā§ āĻĒā§āĻ°āĻĨāĻŽ ā§Š āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĄāĻŋāĻ˛āĻŋāĻ āĻāĻ°āĻ¤ā§ āĻāĻžāĻ:**
```sql
DELETE FROM dummy_employee
ORDER BY id ASC
LIMIT 3;
```
đš **đ Result:** āĻĒā§āĻ°āĻĨāĻŽ ā§Š āĻāĻ¨ āĻāĻ°ā§āĻŽā§ **āĻŽā§āĻā§ āĻ¯āĻžāĻŦā§āĨ¤**
---
## **đĨ āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `LIMIT`**
â **`LIMIT n`** â āĻĒā§āĻ°āĻĨāĻŽ `n` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžā§āĨ¤
â **`LIMIT n OFFSET m`** â āĻĒā§āĻ°āĻĨāĻŽ `m` āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻĒāĻ°ā§āĻ° `n` āĻ°ā§ āĻĻā§āĻāĻžā§āĨ¤
â **`ORDER BY` + `LIMIT`** â āĻŦā§ āĻŦāĻž āĻā§āĻ āĻŽāĻžāĻ¨ā§āĻ° āĻļā§āĻ°ā§āĻˇ `n` āĻāĻž āĻ°ā§ āĻĻā§āĻāĻžāĻ¤ā§ āĻ¸āĻžāĻšāĻžāĻ¯ā§āĻ¯ āĻāĻ°ā§āĨ¤
â **`WHERE` + `LIMIT`** â āĻļāĻ°ā§āĻ¤ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°ā§āĨ¤
â **`DELETE` + `LIMIT`** â āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĄāĻŋāĻ˛āĻŋāĻ āĻāĻ°ā§āĨ¤
---
### **đš SQL-āĻ `OFFSET` āĻā§āĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
đš **`OFFSET` āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ `LIMIT` āĻāĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻšā§, āĻ¯āĻž āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻ¸ā§āĻāĻŋāĻĒ (āĻŦāĻžāĻĻ) āĻāĻ°ā§ āĻĒāĻ°ā§āĻ° āĻĄāĻžāĻāĻž āĻĻā§āĻāĻžāĻ¤ā§ āĻ¸āĻžāĻšāĻžāĻ¯ā§āĻ¯ āĻāĻ°ā§āĨ¤**
đš āĻāĻāĻŋ **āĻĒā§āĻāĻŋāĻ¨ā§āĻļāĻ¨ (pagination)** āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ āĻ
āĻ¨ā§āĻ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§āĨ¤
---
## **â
`LIMIT` vs `LIMIT + OFFSET`**
đ **āĻā§āĻŦāĻ˛ `LIMIT` āĻĻāĻŋāĻ˛ā§:** āĻĒā§āĻ°āĻĨāĻŽ `n` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
đ **`LIMIT + OFFSET` āĻĻāĻŋāĻ˛ā§:** āĻĒā§āĻ°āĻĨāĻŽ `OFFSET` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° `LIMIT` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
## **â
`OFFSET` āĻ¸āĻš `dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻžāĻ āĻāĻ°āĻž**
### **ā§§ī¸âŖ āĻĒā§āĻ°āĻĨāĻŽ ā§Ģ āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĻā§āĻāĻžāĻ¨ā§ (`LIMIT` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§)**
```sql
SELECT * FROM dummy_employee
LIMIT 5;
```
đš **Result:**
| id | name | department | salary |
|----|------|-----------|--------|
| 1 | Arafat | IT | 50000 |
| 2 | Samiul | HR | 40000 |
| 3 | Shuvo | Marketing | 45000 |
| 4 | Alex | Finance | 42000 |
| 5 | John | IT | 46000 |
---
### **ā§¨ī¸âŖ āĻĒā§āĻ°āĻĨāĻŽ ā§ĢāĻāĻŋ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° ā§ĢāĻāĻŋ āĻ°ā§ āĻĻā§āĻāĻžāĻ¨ā§ (`OFFSET` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§)**
```sql
SELECT * FROM dummy_employee
LIMIT 5 OFFSET 5;
```
đš **Result:**
| id | name | department | salary |
|----|--------|-----------|--------|
| 6 | Michael | HR | 39000 |
| 7 | Sarah | IT | 42000 |
| 8 | David | Finance | 41000 |
| 9 | Emma | HR | 43000 |
| 10 | James | IT | 40000 |
đ **āĻāĻāĻžāĻ¨ā§ āĻĒā§āĻ°āĻĨāĻŽ ā§ĢāĻāĻŋ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻā§āĻā§āĻž āĻšā§ā§āĻā§, āĻ¤āĻžāĻ āĻ°ā§āĻāĻžāĻ˛ā§āĻ āĻļā§āĻ°ā§ āĻšā§ā§āĻā§ `id = 6` āĻĨā§āĻā§āĨ¤**
---
### **ā§Šī¸âŖ ā§§ā§ĻāĻāĻŋ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° ā§ĢāĻāĻŋ āĻ°ā§ āĻĻā§āĻāĻžāĻ¨ā§**
```sql
SELECT * FROM dummy_employee
LIMIT 5 OFFSET 10;
```
đš **Result:**
| id | name | department | salary |
|----|------|-----------|--------|
| 11 | Robert | Finance | 45000 |
| 12 | Sophia | HR | 39000 |
| 13 | William | IT | 47000 |
| 14 | Olivia | Marketing | 41000 |
| 15 | Daniel | IT | 43000 |
đ **āĻāĻŦāĻžāĻ° āĻĒā§āĻ°āĻĨāĻŽ ā§§ā§ĻāĻāĻŋ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻā§āĻā§āĻž āĻšā§ā§āĻā§, āĻ¤āĻžāĻ āĻ°ā§āĻāĻžāĻ˛ā§āĻ āĻļā§āĻ°ā§ āĻšā§ā§āĻā§ `id = 11` āĻĨā§āĻā§āĨ¤**
---
## **â
`ORDER BY` + `OFFSET` (āĻŦā§āĻļāĻŋ āĻŦā§āĻ¤āĻ¨ā§āĻ° āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻŽāĻ§ā§āĻ¯ā§ ā§Ģ-ā§§ā§Ļ āĻ¨āĻŽā§āĻŦāĻ° āĻ
āĻŦāĻ¸ā§āĻĨāĻžāĻ¨ā§ āĻĨāĻžāĻāĻž āĻāĻ°ā§āĻŽā§āĻ°āĻž)**
```sql
SELECT * FROM dummy_employee
ORDER BY salary DESC
LIMIT 5 OFFSET 5;
```
đš **Result:**
| id | name | department | salary |
|----|------|-----------|--------|
| 6 | Michael | HR | 39000 |
| 7 | Sarah | IT | 42000 |
| 8 | David | Finance | 41000 |
| 9 | Emma | HR | 43000 |
| 10 | James | IT | 40000 |
đ **āĻāĻāĻžāĻ¨ā§ āĻŦā§āĻļāĻŋ āĻŦā§āĻ¤āĻ¨ā§āĻ° **āĻļā§āĻ°ā§āĻˇ ā§Ģ āĻāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° ā§Ģ āĻāĻ¨āĻā§ āĻĻā§āĻāĻžāĻ¨ā§ āĻšā§ā§āĻā§āĨ¤**
---
## **â
`DELETE` + `OFFSET` (āĻĒā§āĻ°āĻĨāĻŽ ā§Ģ āĻāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° ā§Š āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĄāĻŋāĻ˛āĻŋāĻ āĻāĻ°āĻž)**
```sql
DELETE FROM dummy_employee
ORDER BY id ASC
LIMIT 3 OFFSET 5;
```
đ **āĻāĻ¤ā§ āĻĒā§āĻ°āĻĨāĻŽ ā§Ģ āĻāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° ā§Š āĻāĻ¨ āĻāĻ°ā§āĻŽā§ āĻĄāĻŋāĻ˛āĻŋāĻ āĻšāĻŦā§āĨ¤**
---
## **đĨ āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `OFFSET`**
â **`LIMIT n`** â āĻĒā§āĻ°āĻĨāĻŽ `n` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
â **`LIMIT n OFFSET m`** â āĻĒā§āĻ°āĻĨāĻŽ `m` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻĒāĻ°ā§āĻ° `n` āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻĻā§āĻāĻžāĻŦā§āĨ¤
â **`ORDER BY` + `OFFSET`** â āĻā§āĻ¨ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻā§āĻ°āĻŽā§ (āĻ¸āĻ°ā§āĻŦā§āĻā§āĻ āĻŦāĻž āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨) āĻāĻŋāĻā§ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻĻā§āĻāĻžāĻ¨ā§ āĻ¯āĻžā§āĨ¤
â **`DELETE` + `OFFSET`** â āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ¸āĻāĻā§āĻ¯āĻ āĻ°ā§ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻāĻŋāĻā§ āĻ°ā§ āĻŽā§āĻā§ āĻĢā§āĻ˛āĻž āĻ¯āĻžā§āĨ¤
---
### **đš `GROUP BY` āĻā§āĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
**`GROUP BY`** SQL-āĻāĻ° āĻāĻāĻāĻŋ āĻļāĻā§āĻ¤āĻŋāĻļāĻžāĻ˛ā§ āĻā§āĻ˛āĻ āĻ¯āĻž āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻĄāĻžāĻāĻžāĻā§ āĻāĻ āĻŦāĻž āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§āĻ° āĻāĻŋāĻ¤ā§āĻ¤āĻŋāĻ¤ā§ **āĻā§āĻ°ā§āĻĒ** āĻāĻ°āĻž āĻšā§ āĻāĻŦāĻ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ **āĻ
ā§āĻ¯āĻžāĻā§āĻ°āĻŋāĻā§āĻ āĻĢāĻžāĻāĻļāĻ¨** (āĻ¯ā§āĻŽāĻ¨ `SUM`, `AVG`, `COUNT`, `MIN`, `MAX`) āĻāĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§āĨ¤ āĻāĻāĻŋ āĻāĻĒāĻ¨āĻžāĻā§ āĻĄāĻžāĻāĻž āĻā§āĻ°ā§āĻĒ āĻāĻ°ā§ āĻĒā§āĻ°āĻ¤āĻŋāĻāĻŋ āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻĒāĻ° āĻĢāĻžāĻāĻļāĻ¨ āĻĒā§āĻ°ā§ā§āĻ āĻāĻ°āĻ¤ā§ āĻ¸āĻžāĻšāĻžāĻ¯ā§āĻ¯ āĻāĻ°ā§āĨ¤
---
### **â
`GROUP BY` āĻāĻ° āĻ¸ā§āĻāĻŽā§āĻ¨ā§āĻ:**
1. **`GROUP BY` āĻāĻāĻāĻŋ āĻŦāĻž āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽ āĻ¨āĻŋā§ā§ āĻā§āĻ°ā§āĻĒ āĻāĻ°ā§āĨ¤**
2. **āĻ
ā§āĻ¯āĻžāĻā§āĻ°āĻŋāĻā§āĻ āĻĢāĻžāĻāĻļāĻ¨** āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻĒāĻ° āĻāĻžāĻ āĻāĻ°ā§āĨ¤
3. **`HAVING`** (āĻ¯āĻž `WHERE` āĻāĻ° āĻŽāĻ¤ā§) āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻĒāĻ° āĻļāĻ°ā§āĻ¤ āĻĻā§ā§, āĻāĻŋāĻ¨ā§āĻ¤ā§ `WHERE` āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ°ā§āĻāĻ°ā§āĻĄāĻā§āĻ˛ā§āĻ° āĻāĻĒāĻ° āĻāĻžāĻ āĻāĻ°ā§āĨ¤
---
### **â
āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§§: `GROUP BY` āĻāĻ āĻāĻ˛āĻžāĻŽ āĻĻāĻŋā§ā§**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ **`dummy_employee`** āĻā§āĻŦāĻŋāĻ˛ā§ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° āĻŦā§āĻ¤āĻ¨ āĻĻā§āĻāĻžāĻ¨ā§āĻ° āĻĒāĻžāĻļāĻžāĻĒāĻžāĻļāĻŋ, **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻā§ āĻŦā§āĻ¤āĻ¨** āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĨ¤
#### **`GROUP BY` āĻĻāĻŋā§ā§ `department` āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻā§ āĻŦā§āĻ¤āĻ¨ āĻŦā§āĻ° āĻāĻ°āĻž:**
```sql
SELECT department, AVG(salary) AS avg_salary
FROM dummy_employee
GROUP BY department;
```
đš **Result:**
| department | avg_salary |
|------------|------------|
| IT | 47000.00 |
| HR | 42000.00 |
| Marketing | 43000.00 |
| Finance | 42000.00 |
---
### **â
āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§¨: `GROUP BY` āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽ āĻĻāĻŋā§ā§**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻĒāĻ¨āĻŋ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻāĻŦāĻ āĻŦā§āĻ¤āĻ¨ āĻ
āĻ¨ā§āĻ¸āĻžāĻ°ā§ āĻāĻ°ā§āĻŽā§āĻĻā§āĻ° **āĻāĻŖāĻ¨āĻž** āĻāĻ°āĻ¤ā§ āĻāĻžāĻ¨āĨ¤ āĻāĻĒāĻ¨āĻŋ āĻĻā§āĻāĻŋ āĻāĻ˛āĻžāĻŽ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°ā§āĻ¨ â `department` āĻāĻŦāĻ `salary`āĨ¤
#### **`GROUP BY` āĻĻāĻŋā§ā§ `department` āĻāĻŦāĻ `salary` āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻŽā§āĻ āĻāĻ°ā§āĻŽā§ āĻāĻŖāĻ¨āĻž:**
```sql
SELECT department, salary, COUNT(*) AS total_employees
FROM dummy_employee
GROUP BY department, salary;
```
đš **Result:**
| department | salary | total_employees |
|------------|--------|-----------------|
| IT | 50000 | 2 |
| HR | 39000 | 1 |
| Marketing | 45000 | 1 |
| Finance | 42000 | 1 |
| IT | 46000 | 1 |
| HR | 43000 | 1 |
| Marketing | 41000 | 1 |
---
### **â
`GROUP BY` + `HAVING`**
**`HAVING`** āĻšāĻ˛ āĻāĻāĻāĻŋ āĻļāĻ°ā§āĻ¤ āĻ¯āĻž **`GROUP BY`** āĻāĻ° āĻĒāĻ°ā§ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§, āĻāĻŦāĻ āĻāĻāĻŋ āĻā§āĻ°ā§āĻĒ āĻāĻ°āĻž āĻ°ā§āĻāĻ°ā§āĻĄā§āĻ° āĻāĻĒāĻ° āĻļāĻ°ā§āĻ¤ āĻĒā§āĻ°ā§ā§āĻ āĻāĻ°ā§āĨ¤ āĻāĻāĻŋ **`WHERE`** āĻāĻ° āĻŽāĻ¤ā§ āĻāĻžāĻ āĻāĻ°ā§, āĻ¤āĻŦā§ **`WHERE`** āĻā§āĻŦāĻ˛ āĻ°ā§āĻāĻ°ā§āĻĄā§āĻ° āĻāĻ¨ā§āĻ¯ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§, āĻāĻ° **`HAVING`** āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻ¨ā§āĻ¯āĨ¤
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
āĻ¯āĻĻāĻŋ āĻāĻĒāĻ¨āĻŋ āĻāĻžāĻā§āĻā§āĻ¨, āĻāĻŽāĻ¨ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻāĻā§āĻ˛ā§ āĻĻā§āĻāĻžāĻ¤ā§ āĻ¯ā§āĻāĻžāĻ¨ā§ āĻā§ āĻŦā§āĻ¤āĻ¨ ā§Ēā§Ģā§Ļā§Ļā§Ļ āĻāĻžāĻāĻžāĻ° āĻŦā§āĻļāĻŋ:
```sql
SELECT department, AVG(salary) AS avg_salary
FROM dummy_employee
GROUP BY department
HAVING AVG(salary) > 45000;
```
đš **Result:**
| department | avg_salary |
|------------|------------|
| IT | 47000.00 |
---
### **â
`GROUP BY` + `ORDER BY`**
āĻāĻĒāĻ¨āĻŋ **`GROUP BY`** āĻāĻ° āĻ¸āĻžāĻĨā§ **`ORDER BY`** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻā§āĻ°ā§āĻĒā§āĻ° āĻ°ā§āĻāĻžāĻ˛ā§āĻāĻā§āĻ˛ā§ āĻ¨āĻŋāĻ°ā§āĻĻāĻŋāĻˇā§āĻ āĻ
āĻ°ā§āĻĄāĻžāĻ°ā§ āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻĒāĻžāĻ°ā§āĻ¨āĨ¤
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`department` āĻ
āĻ¨ā§āĻ¯āĻžā§ā§ āĻā§ āĻŦā§āĻ¤āĻ¨ āĻĻā§āĻāĻžāĻ¨ā§āĻ° āĻĒāĻžāĻļāĻžāĻĒāĻžāĻļāĻŋ, `avg_salary` āĻ
āĻ¨ā§āĻ¸āĻžāĻ°ā§ āĻ¸āĻžāĻāĻžāĻ¨ā§:**
```sql
SELECT department, AVG(salary) AS avg_salary
FROM dummy_employee
GROUP BY department
ORDER BY avg_salary DESC;
```
đš **Result:**
| department | avg_salary |
|------------|------------|
| IT | 47000.00 |
| Marketing | 43000.00 |
| Finance | 42000.00 |
| HR | 42000.00 |
---
### **đĨ āĻ¸āĻāĻā§āĻˇā§āĻĒā§ `GROUP BY`:**
- **`GROUP BY column`** â āĻāĻāĻāĻŋ āĻāĻ˛āĻžāĻŽ (āĻŦāĻž āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽ) āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§ āĻ°ā§āĻāĻ°ā§āĻĄāĻā§āĻ˛ā§ āĻā§āĻ°ā§āĻĒ āĻāĻ°ā§āĨ¤
- **`HAVING`** â `GROUP BY` āĻāĻ° āĻĒāĻ°ā§ āĻļāĻ°ā§āĻ¤ āĻĻā§ā§ (āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻĒāĻ°)āĨ¤
- **`ORDER BY`** â āĻā§āĻ°ā§āĻĒāĻā§āĻ˛āĻŋāĻā§ āĻ¸āĻžāĻāĻžāĻ¤ā§ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§āĨ¤
- **āĻ
ā§āĻ¯āĻžāĻā§āĻ°āĻŋāĻā§āĻ āĻĢāĻžāĻāĻļāĻ¨** (āĻ¯ā§āĻŽāĻ¨ `AVG`, `SUM`, `COUNT`, `MIN`, `MAX`) āĻā§āĻ°ā§āĻĒā§āĻ° āĻāĻĒāĻ° āĻāĻžāĻ āĻāĻ°ā§āĨ¤
---
### **đš SQL-āĻ `MIN`, `MAX`, `COUNT`, `AVG`, `SUM` āĻĢāĻžāĻāĻļāĻ¨**
āĻāĻ āĻĢāĻžāĻāĻļāĻ¨āĻā§āĻ˛ā§ SQL āĻ **āĻ
ā§āĻ¯āĻžāĻā§āĻ°āĻŋāĻā§āĻ āĻĢāĻžāĻāĻļāĻ¨** (Aggregate Functions) āĻšāĻŋāĻ¸ā§āĻŦā§ āĻĒāĻ°āĻŋāĻāĻŋāĻ¤, āĻ¯ā§āĻā§āĻ˛āĻŋ āĻĄāĻžāĻāĻžāĻ° āĻāĻĒāĻ° āĻāĻŖāĻ¨āĻž āĻāĻ°āĻžāĻ° āĻāĻ¨ā§āĻ¯ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§āĨ¤ āĻāĻā§āĻ˛ā§ āĻ¸āĻžāĻ§āĻžāĻ°āĻŖāĻ¤ **`GROUP BY`** āĻāĻŦāĻ **`WHERE`** āĻāĻ° āĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§, āĻāĻŋāĻ¨ā§āĻ¤ā§ āĻāĻāĻāĻāĻžāĻŦā§ āĻĄāĻžāĻāĻžāĻ° āĻŽā§āĻāĻžāĻŽā§āĻāĻŋ āĻāĻā§āĻ¸āĻā§āĻ°ā§āĻ¯āĻžāĻā§āĻ āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°āĻž āĻ¯āĻžā§āĨ¤
---
### **â
ā§§. `MIN` (āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨ āĻŽāĻžāĻ¨)**
đš **`MIN` āĻĢāĻžāĻāĻļāĻ¨ āĻāĻāĻāĻŋ āĻāĻ˛āĻžāĻŽā§ āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨ āĻŽāĻžāĻ¨ āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°ā§āĨ¤**
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `salary` āĻāĻ˛āĻžāĻŽ āĻĨā§āĻā§ āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨ āĻŦā§āĻ¤āĻ¨ āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°āĻž:**
```sql
SELECT MIN(salary) AS min_salary FROM dummy_employee;
```
đš **Result:**
| min_salary |
|------------|
| 39000 |
---
### **â
ā§¨. `MAX` (āĻ¸āĻ°ā§āĻŦā§āĻā§āĻ āĻŽāĻžāĻ¨)**
đš **`MAX` āĻĢāĻžāĻāĻļāĻ¨ āĻāĻāĻāĻŋ āĻāĻ˛āĻžāĻŽā§ āĻ¸āĻ°ā§āĻŦā§āĻā§āĻ āĻŽāĻžāĻ¨ āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°ā§āĨ¤**
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `salary` āĻāĻ˛āĻžāĻŽ āĻĨā§āĻā§ āĻ¸āĻ°ā§āĻŦā§āĻā§āĻ āĻŦā§āĻ¤āĻ¨ āĻā§āĻāĻā§ āĻŦā§āĻ° āĻāĻ°āĻž:**
```sql
SELECT MAX(salary) AS max_salary FROM dummy_employee;
```
đš **Result:**
| max_salary |
|------------|
| 50000 |
---
### **â
ā§Š. `COUNT` (āĻĄāĻžāĻāĻž āĻ¸āĻāĻā§āĻ¯āĻž āĻā§āĻ¨āĻž)**
đš **`COUNT` āĻĢāĻžāĻāĻļāĻ¨ āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§ āĻŽā§āĻ āĻ°ā§āĻāĻ°ā§āĻĄā§āĻ° āĻ¸āĻāĻā§āĻ¯āĻž āĻāĻŖāĻ¨āĻž āĻāĻ°ā§āĨ¤**
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° āĻŽā§āĻ āĻāĻ°ā§āĻŽā§āĻ° āĻ¸āĻāĻā§āĻ¯āĻž āĻāĻžāĻ¨āĻžāĻ° āĻāĻ¨ā§āĻ¯:**
```sql
SELECT COUNT(*) AS total_employees FROM dummy_employee;
```
đš **Result:**
| total_employees |
|-----------------|
| 15 |
---
### **â
ā§Ē. `AVG` (āĻā§ āĻŽāĻžāĻ¨)**
đš **`AVG` āĻĢāĻžāĻāĻļāĻ¨ āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§āĻ° āĻā§ āĻŽāĻžāĻ¨ āĻŦā§āĻ° āĻāĻ°ā§āĨ¤**
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `salary` āĻāĻ˛āĻžāĻŽā§āĻ° āĻā§ āĻŦā§āĻ¤āĻ¨ āĻŦā§āĻ° āĻāĻ°āĻž:**
```sql
SELECT AVG(salary) AS avg_salary FROM dummy_employee;
```
đš **Result:**
| avg_salary |
|------------|
| 43500.00 |
---
### **â
ā§Ģ. `SUM` (āĻŽā§āĻ āĻŽāĻžāĻ¨)**
đš **`SUM` āĻĢāĻžāĻāĻļāĻ¨ āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§ āĻ¸āĻŦ āĻŽāĻžāĻ¨ā§āĻ° āĻ¯ā§āĻāĻĢāĻ˛ āĻŦā§āĻ° āĻāĻ°ā§āĨ¤**
#### **āĻāĻĻāĻžāĻšāĻ°āĻŖ:**
**`dummy_employee` āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `salary` āĻāĻ˛āĻžāĻŽā§āĻ° āĻŽā§āĻ āĻŦā§āĻ¤āĻ¨ āĻŦā§āĻ° āĻāĻ°āĻž:**
```sql
SELECT SUM(salary) AS total_salary FROM dummy_employee;
```
đš **Result:**
| total_salary |
|--------------|
| 652500 |
---
### **đ āĻāĻāĻ¤ā§āĻ°ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ°**
**āĻ¯āĻĻāĻŋ āĻ¸āĻŦ āĻĢāĻžāĻāĻļāĻ¨ āĻāĻāĻ¸āĻžāĻĨā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻāĻžāĻ¨:**
```sql
SELECT
MIN(salary) AS min_salary,
MAX(salary) AS max_salary,
COUNT(*) AS total_employees,
AVG(salary) AS avg_salary,
SUM(salary) AS total_salary
FROM dummy_employee;
```
đš **Result:**
| min_salary | max_salary | total_employees | avg_salary | total_salary |
|------------|------------|-----------------|------------|--------------|
| 39000 | 50000 | 15 | 43500.00 | 652500 |
---
### **đĨ āĻ¸āĻāĻā§āĻˇā§āĻĒā§ āĻĢāĻžāĻāĻļāĻ¨āĻā§āĻ˛ā§:**
- **`MIN(column)`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¸āĻ°ā§āĻŦāĻ¨āĻŋāĻŽā§āĻ¨ āĻŽāĻžāĻ¨āĨ¤
- **`MAX(column)`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¸āĻ°ā§āĻŦā§āĻā§āĻ āĻŽāĻžāĻ¨āĨ¤
- **`COUNT(*)`** â āĻŽā§āĻ āĻ°ā§āĻāĻ°ā§āĻĄ āĻ¸āĻāĻā§āĻ¯āĻžāĨ¤
- **`AVG(column)`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻā§ āĻŽāĻžāĻ¨āĨ¤
- **`SUM(column)`** â āĻāĻ˛āĻžāĻŽā§āĻ° āĻ¸āĻŦ āĻŽāĻžāĻ¨ā§āĻ° āĻ¯ā§āĻāĻĢāĻ˛āĨ¤
---
### **đš `DISTINCT` āĻā§āĻāĻžāĻŦā§ āĻāĻžāĻ āĻāĻ°ā§?**
SQL-āĻ **`DISTINCT`** āĻāĻāĻāĻŋ āĻāĻŋāĻā§āĻžāĻ°ā§āĻĄ āĻ¯āĻž **āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ (āĻĒā§āĻ¨āĻ°āĻžāĻŦā§āĻ¤ā§āĻ¤) āĻŽāĻžāĻ¨** āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§, āĻāĻāĻ āĻŦāĻž āĻ
āĻ¨āĻ¨ā§āĻ¯ (unique) āĻŽāĻžāĻ¨āĻā§āĻ˛ā§ āĻĒā§āĻ°āĻĻāĻ°ā§āĻļāĻ¨ āĻāĻ°ā§āĨ¤ āĻāĻāĻŋ āĻŽā§āĻ˛āĻ¤ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻĄā§āĻāĻž āĻĢāĻŋāĻ˛ā§āĻāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻŦā§āĻ¯āĻŦāĻšā§āĻ¤ āĻšā§ āĻāĻŦāĻ āĻāĻĒāĻ¨āĻŋ āĻ¯ā§āĻā§āĻ¨ā§ āĻāĻ˛āĻžāĻŽā§ āĻŦāĻž āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§ **āĻĄāĻŋāĻ¸ā§āĻāĻŋāĻāĻā§āĻ** āĻŽāĻžāĻ¨ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĻ˛ā§ āĻāĻāĻŋ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ¤ā§ āĻĒāĻžāĻ°ā§āĻ¨āĨ¤
---
### **â
`DISTINCT` āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ°:**
**`DISTINCT`** āĻāĻŋāĻā§āĻžāĻ°ā§āĻĄāĻāĻŋ āĻāĻĒāĻ¨āĻŋ **`SELECT`** āĻā§āĻāĻ°āĻŋ āĻĻāĻŋā§ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§āĻ¨, āĻāĻŦāĻ āĻāĻāĻŋ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻŽāĻžāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻĢāĻ˛āĻžāĻĢāĻ˛ āĻĻā§āĻāĻžā§āĨ¤
---
### **â
āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§§: āĻāĻ āĻāĻ˛āĻžāĻŽā§ āĻĄāĻŋāĻ¸ā§āĻāĻŋāĻāĻā§āĻ āĻŽāĻžāĻ¨**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻĒāĻ¨āĻŋ **`dummy_employee`** āĻā§āĻŦāĻŋāĻ˛ā§āĻ° `department` āĻāĻ˛āĻžāĻŽ āĻĨā§āĻā§ āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ
āĻ¨āĻ¨ā§āĻ¯ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻāĻā§āĻ˛ā§ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻ¨āĨ¤
```sql
SELECT DISTINCT department FROM dummy_employee;
```
đš **Result:**
| department |
|------------|
| IT |
| HR |
| Marketing |
| Finance |
āĻāĻāĻžāĻ¨ā§ **`DISTINCT`** āĻāĻŋāĻā§āĻžāĻ°ā§āĻĄāĻāĻŋ **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ** āĻāĻ˛āĻžāĻŽā§ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻŽāĻžāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§āĻā§ āĻāĻŦāĻ āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻ
āĻ¨āĻ¨ā§āĻ¯ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻ¨āĻžāĻŽāĻā§āĻ˛ā§ āĻĻā§āĻāĻŋā§ā§āĻā§āĨ¤
---
### **â
āĻāĻĻāĻžāĻšāĻ°āĻŖ ā§¨: āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§ āĻĄāĻŋāĻ¸ā§āĻāĻŋāĻāĻā§āĻ āĻŽāĻžāĻ¨**
āĻāĻĒāĻ¨āĻŋ **`department`** āĻāĻŦāĻ **`salary`** āĻāĻ˛āĻžāĻŽ āĻĻā§āĻā§āĻ¤ā§ **āĻĄāĻŋāĻ¸ā§āĻāĻŋāĻāĻā§āĻ** āĻŽāĻžāĻ¨ āĻĻā§āĻāĻ¤ā§ āĻāĻžāĻāĻ˛ā§:
```sql
SELECT DISTINCT department, salary FROM dummy_employee;
```
đš **Result:**
| department | salary |
|------------|--------|
| IT | 50000 |
| HR | 39000 |
| Marketing | 45000 |
| Finance | 42000 |
| IT | 46000 |
| HR | 43000 |
āĻāĻāĻžāĻ¨ā§, **`DISTINCT`** āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻāĻŦāĻ āĻŦā§āĻ¤āĻ¨ā§āĻ° āĻāĻāĻ¨āĻŋāĻ (āĻ
āĻ¨āĻ¨ā§āĻ¯) āĻāĻŽā§āĻŦāĻŋāĻ¨ā§āĻļāĻ¨āĻā§āĻ˛ā§ āĻĻā§āĻāĻŋā§ā§āĻā§, āĻ
āĻ°ā§āĻĨāĻžā§ **āĻāĻāĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ āĻāĻŦāĻ āĻŦā§āĻ¤āĻ¨ āĻāĻāĻžāĻ§āĻŋāĻ āĻŦāĻžāĻ° āĻ¨āĻž āĻĻā§āĻāĻŋā§ā§, āĻāĻāĻŦāĻžāĻ° āĻĻā§āĻāĻŋā§ā§āĻā§āĨ¤**
---
### **â
`DISTINCT` + `COUNT`**
āĻ§āĻ°āĻž āĻ¯āĻžāĻ, āĻāĻĒāĻ¨āĻŋ **āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¸āĻāĻā§āĻ¯āĻž** āĻāĻžāĻ¨āĻžāĻ¤ā§ āĻāĻžāĻ¨, āĻāĻŋāĻ¨ā§āĻ¤ā§ āĻāĻāĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻāĻ¨ā§āĻ¯ āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ°ā§āĻŽā§ āĻĨāĻžāĻāĻ˛ā§āĻ, āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° **āĻ
āĻ¨āĻ¨ā§āĻ¯** āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻā§āĻ° āĻ¸āĻāĻā§āĻ¯āĻž āĻāĻžāĻāĻā§āĻ¨āĨ¤
```sql
SELECT COUNT(DISTINCT department) AS unique_departments
FROM dummy_employee;
```
đš **Result:**
| unique_departments |
|--------------------|
| 4 |
āĻāĻāĻžāĻ¨ā§ **`COUNT(DISTINCT department)`** **āĻĄāĻŋāĻ¸ā§āĻāĻŋāĻāĻā§āĻ āĻĄāĻŋāĻĒāĻžāĻ°ā§āĻāĻŽā§āĻ¨ā§āĻ** āĻā§āĻ¨ā§ āĻ¸āĻāĻā§āĻ¯āĻž āĻĻā§āĻāĻŋā§ā§āĻā§āĨ¤
---
### **đ `DISTINCT` āĻāĻ° āĻāĻŋāĻā§ āĻā§āĻ°ā§āĻ¤ā§āĻŦāĻĒā§āĻ°ā§āĻŖ āĻĒā§ā§āĻ¨ā§āĻ:**
- **āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽ:** āĻ¯āĻĻāĻŋ āĻāĻĒāĻ¨āĻŋ āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§ **`DISTINCT`** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°ā§āĻ¨, āĻ¤āĻžāĻšāĻ˛ā§ āĻā§āĻŦāĻ˛āĻŽāĻžāĻ¤ā§āĻ° āĻ āĻāĻ˛āĻžāĻŽā§āĻ° **āĻāĻŽā§āĻŦāĻŋāĻ¨ā§āĻļāĻ¨** āĻšāĻŋāĻ¸ā§āĻŦā§āĻ āĻ
āĻ¨āĻ¨ā§āĻ¯ (unique) āĻŽāĻžāĻ¨ āĻĻā§āĻāĻžāĻŦā§āĨ¤
- **`DISTINCT`** āĻā§āĻŦāĻ˛ **`SELECT`** āĻā§āĻāĻ°āĻŋāĻ¤ā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻšā§, āĻĄā§āĻāĻž āĻĒāĻ°āĻŋāĻŦāĻ°ā§āĻ¤āĻ¨ āĻŦāĻž āĻŽā§āĻā§ āĻĢā§āĻ˛āĻžāĻ° āĻā§āĻˇā§āĻ¤ā§āĻ°ā§ āĻ¨ā§āĨ¤
- **āĻā§āĻ¨ā§ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻ¨āĻž āĻĨāĻžāĻāĻ˛ā§:** āĻ¯āĻāĻ¨ āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻŽāĻžāĻ¨ āĻĨāĻžāĻā§ āĻ¨āĻž, āĻ¤āĻāĻ¨ `DISTINCT` āĻāĻžāĻ āĻāĻ°āĻŦā§ āĻ¨āĻž āĻāĻŦāĻ **āĻ¸āĻžāĻ§āĻžāĻ°āĻŖ `SELECT`** āĻā§āĻāĻ°āĻŋāĻ° āĻŽāĻ¤ āĻ°ā§āĻāĻžāĻ˛ā§āĻ āĻĻā§āĻāĻžāĻŦā§āĨ¤
---
### **đĨ āĻ¸āĻāĻā§āĻˇā§āĻĒā§:**
- **`DISTINCT`** â āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻŽāĻžāĻ¨ āĻŦāĻžāĻĻ āĻĻāĻŋā§ā§ āĻ
āĻ¨āĻ¨ā§āĻ¯ (unique) āĻŽāĻžāĻ¨ āĻĻā§āĻāĻžā§āĨ¤
- āĻāĻāĻ āĻāĻ˛āĻžāĻŽ āĻŦāĻž āĻāĻāĻžāĻ§āĻŋāĻ āĻāĻ˛āĻžāĻŽā§ āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻž āĻ¯āĻžā§āĨ¤
- **`DISTINCT`** āĻŦā§āĻ¯āĻŦāĻšāĻžāĻ° āĻāĻ°āĻ˛ā§, āĻĄā§āĻĒā§āĻ˛āĻŋāĻā§āĻ āĻŽāĻžāĻ¨ āĻŦāĻžāĻĻ āĻĻā§āĻā§āĻž āĻšā§ āĻāĻŦāĻ āĻĢāĻ˛āĻžāĻĢāĻ˛ āĻšāĻŋāĻ¸ā§āĻŦā§ āĻļā§āĻ§ā§āĻŽāĻžāĻ¤ā§āĻ° āĻāĻāĻ āĻŦāĻž āĻ
āĻ¨āĻ¨ā§āĻ¯ āĻŽāĻžāĻ¨ āĻĒā§āĻ°āĻĻāĻ°ā§āĻļāĻŋāĻ¤ āĻšā§āĨ¤
---