https://github.com/k-sameer701/mysql-cheatsheet
MySql CheatSheet is a condensed guide that provides a quick overview of essential SQL commands and their syntax for MySQL databases. It is a handy resource for developers.
https://github.com/k-sameer701/mysql-cheatsheet
mysql mysqldata mysqldatabase sql
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MySql CheatSheet is a condensed guide that provides a quick overview of essential SQL commands and their syntax for MySQL databases. It is a handy resource for developers.
- Host: GitHub
- URL: https://github.com/k-sameer701/mysql-cheatsheet
- Owner: k-sameer701
- Created: 2024-01-10T12:53:06.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2024-01-11T12:39:33.000Z (over 2 years ago)
- Last Synced: 2025-01-13T23:41:03.488Z (over 1 year ago)
- Topics: mysql, mysqldata, mysqldatabase, sql
- Homepage:
- Size: 104 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
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Metadata Files:
- Readme: README.md
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README
# 🐈⬛ MySql-CheatSheet
## ⛄ Table of Content
* [🌱 Introduction](#Introduction)
* [🌱 Database-Table](#Database-Table)
* [🌱 Inserting-Data](#Inserting-Data)
* [🌱 Select-And-Where](#Select-And-Where)
* [🌱 Constraints](#Constraints)
* [🌱 AND-OR-NOT](#AND-OR-NOT)
* [🌱 In-Operator](#In-Operator)
* [🌱 LIKE-Operator](#LIKE-Operator)
* [🌱 Between-NOT-Between](#Between-NOT-Between)
* [🌱 Order-By-And-Distinct](#Order-By-And-Distinct)
* [🌱 Is-Null-And-Is-Not-Null](#Is-Null-And-Is-Not-Null)
* [🌱 Limit-And-Offset](#Limit-And-Offset)
* [🌱 Aggregate-Functions](#Aggregate-Functions)
* [🌱 Update-Query](#Update-Query)
* [🌱 Delete-Query](#Delete-Query)
* [🌱 Primary-And-Foreign-Key](#Primary-And-Foreign-Key)
* [🌱 Joins](#Joins)
* [🌱 Sub-Query](#Sub-Query)
* [🌱 Exists-And-Not-Exists](#Exists-And-Not-Exists)
## Introduction
## ☘️ What is a database?
`A database is an organized collection of structured information or data.`
## ☘️ What is DBMS?
`Database Management Systems (DBMS) are software systems used to store, retrieve, and run queries on data.`
It is of two types:
- `Relational (SQL)`
A relational database is a collection of data items with pre-defined relationships between them, stored in the form of tables, rows, and columns.
Examples: MySQL, Oracle, PostgreSQL.
- `Non-Relational (No-SQL)`
NoSQL databases are non-relational, offering flexible schemas, scalability, and support for diverse data models. Commonly used in web development, analytics, and content management for handling large and dynamic data.
Examples: MongoDB, Cassandra, Redis.
## ☘️ What is MySQL?
`MySQL is a relational database management system (RDBMS) developed by Oracle i.e. based on structured query language (SQL).`
## Database-Table
## ☘️ What is a database table?
`A database table is a collection of rows and columns that contains relational data.`
### 👻 Create a Database:
#### 🔥 Syntax:
CREATE DATABASE database_name;
#### 👀 Example:
CREATE DATABASE mydatabase;
### 👻 Switch to the Created Database:
#### 🔥 Syntax:
USE database_name;
#### 👀 Example:
USE mydatabase;
### 👻 Create Tables:
Define table structure with columns and data types.
#### 🔥 Syntax:
CREATE TABLE table_name
(
column1 datatype1,
column2 datatype2,
...
);
#### 👀 Example:
CREATE TABLE users
(
id int unsigned,
name varchar(100),
email varchar(150),
password varchar(100),
contact varchar(15),
address text,
dob date,
gender enum("M", "F", "O"),
status boolean
);
#### 👻 Categories of DataTypes in SQL:
- Strings
- Numeric
- Date & Time
`💀 String Data Types`
1. **CHAR(n):**
Fixed-length character string.
2. **VARCHAR(n):**
Variable-length character string.
3. **TEXT:**
Variable-length character string with no specified limit.
4. **TINYTEXT:**
A very small variable-length character string.
5. **MEDIUMTEXT:**
A medium-sized variable-length character string.
6. **LONGTEXT:**
A long variable-length character string.
7. **BINARY(n):**
Fixed-length binary string.
8. **VARBINARY(n):**
Variable-length binary string.
9. **BLOB:**
Variable-length binary large object.
10. **TINYBLOB:**
A very small variable-length binary large object.
11. **MEDIUMBLOB:**
A medium-sized variable-length binary large object.
12. **LONGBLOB:**
A long variable-length binary large object.
13. **ENUM('value1', 'value2', ...):**
Enumerated type, representing one of a predefined set of values.
14. **SET('value1', 'value2', ...):**
Set type, representing a collection of values chosen from a predefined set.
`💀 Number Data Types`
1. **INTEGER or INT:**
Represents whole numbers.
2. **TINYINT:**
A very small integer.
3. **SMALLINT:**
Small-sized integer.
4. **MEDIUMINT:**
Medium-sized integer.
5. **BIGINT:**
Large-sized integer.
6. **DECIMAL(p, s) or NUMERIC(p, s):**
Fixed-point decimal numbers with precision (total digits) and scale (decimal places).
7. **FLOAT(p):**
Floating-point number with single-precision.
8. **DOUBLE(p):**
Floating-point number with double-precision.
9. **REAL:**
A synonym for DOUBLE.
10. **BIT(n):**
A bit-field type, representing a fixed number of bits.
`💀 Date-Time Data Types`
In MySQL, the specific date and time data types include:
1. **DATE:**
Represents a date in the format YYYY-MM-DD.
2. **TIME:**
Represents a time of day in the format HH:MM:SS.
3. **DATETIME:**
Represents a combination of date and time in the format YYYY-MM-DD HH:MM:SS.
4. **TIMESTAMP:**
Similar to DATETIME but with a narrower range and automatically converts to the current timestamp on insert or update.
5. **YEAR:**
Represents a four-digit year value.
## Inserting-Data
## ☘️ Inserting Single Row
🔥 Syntax:
INSERT INTO table_name
(column1, column2, column3, ...)
VALUES
(value1, value2, value3, ...);
👀 Example:
INSERT INTO users
(id, name, email, password, contact, address, dob, gender, status)
VALUES
(1, 'John Doe', 'john@example.com', 'hashed_password', '+123456789', '123 Main St, City', '1990-01-15', 'M', 1);
## ☘️ Inserting Multiple Rows
🔥 Syntax:
INSERT INTO table_name
(column1, column2, column3, ...)
VALUES
(value1, value2, value3, ...),
(value1, value2, value3, ...),
(value1, value2, value3, ...)
👀 Example:
INSERT INTO users
(id, name, email, password, contact, address, dob, gender, status)
VALUES
(2, 'Jane Smith', 'jane@example.com', 'hashed_password2', '+987654321', '456 Oak St, Town', '1995-03-22', 'F', 1),
(3, 'Alex Johnson', 'alex@example.com', 'hashed_password3', '+1122334455', '789 Pine St, Village', '1988-07-10', 'M', 0),
(4, 'Avery Taylor', 'avery@example.com', 'hashed_password4', '+9988776655', '321 Elm St, City', '2000-09-05', 'O', 1),
(5, 'Chris Anderson', 'chris@example.com', 'hashed_password5', '+1122334466', '567 Birch St, Town', '1992-12-18', 'M', 0),
(6, 'Taylor Davis', 'taylor@example.com', 'hashed_password6', '+1122334477', '876 Maple St, Village', '1985-05-30', 'F', 1);
## Select-And-Where
## ☘️ SELECT Statement
`In MySQL, you use the SELECT statement to retrieve data from one or more tables. `
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name;
👀 Example:
SELECT name, email
FROM users;
If you want to select all columns from a table, you can use the wildcard *
🔥 Syntax:
SELECT *
FROM table_name;
👀 Example:
SELECT *
FROM users;
## ☘️ WHERE Clause
`The WHERE clause is used to filter records.`
`It is used to extract only those records that fulfill a specified condition.`
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE condition
👀 Example:
SELECT id, name, email
FROM users
WHERE gender = 'M' AND status = 1;
## ☘️ WHERE Conditions
`In SQL, the WHERE clause is used to filter the rows returned by a query based on specified conditions. Here are common conditions that can be used in conjunction with the WHERE clause:`
1. **Equality (`=`):**
- Used to filter rows where a specified column is equal to a specific value.
- Example: `WHERE column_name = value;`
2. **Inequality (`!=` or `<>`):**
- Used to filter rows where a specified column is not equal to a specific value.
- Example: `WHERE column_name <> value;`
3. **Comparison Operators (`<`, `>`, `<=`, `>=`):**
- Used to filter rows based on numerical or date comparisons.
- Example: `WHERE column_name > value;`
4. **LIKE Operator:**
- Used to perform pattern matching with wildcard characters (`%` for any sequence of characters, `_` for a single character).
- Example: `WHERE column_name LIKE 'pattern';`
5. **BETWEEN Operator:**
- Used to filter rows within a specified range.
- Example: `WHERE column_name BETWEEN value1 AND value2;`
6. **IN Operator:**
- Used to filter rows where a column matches any value in a specified list.
- Example: `WHERE column_name IN (value1, value2, ...);`
7. **IS NULL and IS NOT NULL:**
- Used to filter rows where a column is (or is not) NULL.
- Example: `WHERE column_name IS NULL;`
8. **Logical Operators (AND, OR, NOT):**
- Used to combine multiple conditions.
- Example: `WHERE condition1 AND condition2;`
9. **EXISTS Operator:**
- Used to check if a subquery returns any results.
- Example: `WHERE EXISTS (SELECT * FROM another_table WHERE condition);`
10. **ANY and ALL Operators:**
- Used with subqueries for comparing values.
- Example: `WHERE column_name > ANY (SELECT column_name FROM another_table);`
## ☘️ ALIAS
`In SQL, an alias is a temporary name. It is used to provide a more readable or meaningful name to a table or column, especially when dealing with complex queries or when working with the result of a query.`
There are two main types of aliases:
1. **Table Alias:**
- Used to give a table a temporary, alternative name in a query.
- 🔥 Syntax:
SELECT column1, column2, ...
FROM table_name AS alias_name
WHERE condition;
- 👀 Example:
SELECT name, id
FROM users AS Active_Users
WHERE status = 1;
2. **Column Alias:**
- Used to assign a temporary name to a column in the result set.
- 🔥 Syntax:
SELECT column_name AS alias_name, ...
FROM table_name
WHERE condition;
- 👀 Example:
SELECT name AS E_Name, id AS U_ID
FROM users
WHERE status = 1;
## Constraints
## Table without Constraints 👇
In MySQL, table constraints are rules or conditions applied to the columns in a table to maintain the integrity, accuracy, and relationships of the data.
They are specified during the table creation using the `CREATE TABLE` statement. Constraints can also be added or modified later using the `ALTER TABLE` statement.
1. **PRIMARY KEY Constraint:**
- Ensures that a column or a combination of columns uniquely identifies each row in the table.
- 👀 Example:
CREATE TABLE employees (
employee_id INT PRIMARY KEY,
first_name VARCHAR(50),
last_name VARCHAR(50)
);
2. **FOREIGN KEY Constraint:**
- Establishes a link between two tables, enforcing referential integrity.
- 👀 Example:
CREATE TABLE orders (
order_id INT PRIMARY KEY,
customer_id INT,
FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
);
3. **UNIQUE Constraint:**
- Ensures that all values in a column (or a combination of columns) are unique.
- 👀 Example:
CREATE TABLE products (
product_name VARCHAR(100) UNIQUE,
price DECIMAL(10, 2)
);
4. **CHECK Constraint:**
- Specifies a condition that must be satisfied for each row in the table.
- 👀 Example:
CREATE TABLE employees (
employee_id INT,
salary DECIMAL(10, 2) CHECK (salary >= 0)
);
5. **DEFAULT Constraint:**
- Provides a default value for a column if no value is specified during an INSERT operation.
- 👀 Example:
CREATE TABLE students
(
id INT NOT NULL UNIQUE,
name VARCHAR(100) NOT NULL,
email VARCHAR(150) NOT NULL UNIQUE,
age TINYINT CHECK (age >= 18),
status BOOLEAN DEFAULT 1
);
6. **NOT NULL Constraint:**
- Ensures that a column cannot have a NULL value.
- 👀 Example:
CREATE TABLE orders (
order_id INT,
order_date DATE NOT NULL
);
## AND-OR-NOT
1. **AND Operator:**
- The `AND` operator is used to retrieve rows that satisfy multiple conditions simultaneously.
- 👀 Example: Retrieve students who are both active (`status = 1`) and have an age greater than or equal to 20.
SELECT *
FROM students
WHERE status = 1 AND age >= 20;
2. **OR Operator:**
- The `OR` operator is used to retrieve rows that satisfy at least one of multiple conditions.
- 👀 Example: Retrieve students who are either inactive (`status = 0`) or have an age less than 18.
SELECT *
FROM students
WHERE status = 0 OR age < 18;
3. **NOT Operator:**
- The `NOT` operator is used to negate a condition, retrieving rows that do not satisfy a particular condition.
- 👀 Example: Retrieve students who are not active (`status = 0`).
SELECT *
FROM students
WHERE NOT status = 0;
## In-Operator
## ☘️ IN Operator
`The SQL IN operator is used to specify multiple values in a WHERE clause for a SELECT, UPDATE, DELETE, or INSERT statement. It is typically used to reduce the use of multiple OR conditions in a query.`
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE column_name IN (value1, value2, ...);
- `column1, column2, ...`: The columns you want to retrieve in the SELECT statement.
- `table_name`: The name of the table from which to retrieve the data.
- `column_name`: The column against which you want to compare values.
- `(value1, value2, ...)`: The list of values to compare with the specified column.
👀 Example:
SELECT *
FROM students
WHERE age IN (19,20);
## LIKE-Operator
## ☘️ LIKE Operator
The LIKE Operator is used in a WHERE Clause to search for a specified pattern in a column.
- The percent sign (%) represents zero, one, or multiple characters.
- The underscore sign (_) represents one, single character.
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE column_name LIKE pattern;
👀 Example:
SELECT name
FROM students
WHERE name LIKE "a%";
## Patterns
'a%' : Starts with "a".
'%a' : End with "a".
'%or%' : Have "or" in any position.
'_r%' : Have "r" in the second position.
'a_%' : Starts with "a" and are at least 2 characters in length (including a).
'a__%' : Starts with "a" and are at least 3 characters in length (including a).
'a%o' : Starts with "a" and ends with "o".
## Between-NOT-Between
## ☘️ BETWEEN & NOT BETWEEN
`The BETWEEN and NOT BETWEEN operators in SQL are used to filter the result set based on a range of values. These operators are typically used in the WHERE clause of a SQL query.`
🔥 Syntax (BETEEN):
SELECT column1, column2, ...
FROM table_name
WHERE column_name BETWEEN value1 AND value2;
👀 Example:
SELECT *
FROM students
WHERE age BETWEEN 20 AND 30;
🔥 Syntax (NOT BETWEEN):
SELECT column1, column2, ...
FROM table_name
WHERE column_name NOT BETWEEN value1 AND value2;
👀 Example:
SELECT *
FROM students
WHERE age NOT BETWEEN 20 AND 30;
## Order-By-And-Distinct
## ☘️ ORDER BY
`The ORDER BY clause in SQL is used to sort the result set of a query based on one or more columns. It is typically used at the end of a SELECT statement.`
`Remember that you can sort in ascending order (ASC) or descending order (DESC). If you don't specify the order, ASC is assumed by default. `
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE condition
ORDER BY column1 [ASC | DESC], column2 [ASC | DESC], ...;
👀 Example :
SELECT id, name, age, status
FROM students
ORDER BY age ASC;
## ☘️ DISTINCT
`The DISTINCT keyword in SQL is used in a SELECT statement to eliminate duplicate rows from the result set. It returns only unique values for the specified columns.`
🔥 Syntax:
SELECT DISTINCT column1, column2, ...
FROM table_name
WHERE condition;
👀 Example:
SELECT DISTINCT status
FROM students;
## Is-Null-And-Is-Not-Null
## ☘️ IS NULL
`The IS NULL operator is used to filter rows where a specified column contains a null value.`
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NULL;
👀 Example:
SELECT *
FROM students
WHERE age IS NULL;
## ☘️ IS NOT NULL
`The IS NOT NULL operator is used to filter rows where a specified column does not contain a null value.`
🔥 Syntax:
SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NOT NULL;
👀 Example:
SELECT *
FROM students
WHERE age IS NOT NULL;
## Limit-And-Offset
## ☘️ LIMIT
`If want to LIMIT, the number of results that are returned you can simply use the LIMIT command with several rows to LIMIT by.`
🔥 Syntax:
SELECT *
FROM table_name
LIMIT number_to_limit_by;
👀 Example:
SELECT *
FROM students
LIMIT 3;
## ☘️ OFFSET
`You can also specify an OFFSET from where to start returning the Data.`
🔥 Syntax:
SELECT *
FROM table_name
LIMIT number_to_limit_by OFFSET number_of_rows_to_skip;
👀 Example:
SELECT *
FROM students
LIMIT 3 OFFSET 2;
## Aggregate-Functions
## ☘️ AGGREGATE FUNCTIONS
`In MySQL, aggregate functions are used to perform a calculation on a set of values and return a single value.`
Here are some common aggregate functions in MySQL:
1. **COUNT():**
- Counts the number of rows in a result set.
🔥 Syntax:
SELECT COUNT(column_name) FROM table_name WHERE condition;
2. **SUM():**
- Calculates the sum of values in a numeric column.
🔥 Syntax:
SELECT SUM(column_name) FROM table_name WHERE condition;
3. **AVG():**
- Calculates the average of values in a numeric column.
🔥 Syntax:
SELECT AVG(column_name) FROM table_name WHERE condition;
4. **MIN():**
- Finds the minimum value in a column.
🔥 Syntax:
SELECT MIN(column_name) FROM table_name WHERE condition;
5. **MAX():**
- Finds the maximum value in a column.
🔥 Syntax:
SELECT MAX(column_name) FROM table_name WHERE condition;
👀 Example:
SELECT
SUM() AS total_sales,
AVG(sale_amount) AS average_sale,
COUNT(order_id) AS order_count
FROM sales
WHERE sale_date >= '2022-01-01';
## Update-Query
## 🌱 UPDATE
- `An update query is a database operation that modifies existing records in a table.`
- `Specify a condition that determines which records to update. If you omit the WHERE clause, all records in the table will be updated.`
🔥 Syntax:
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
👀 Example:
UPDATE employees
SET salary = salary * 1.1
WHERE bonus > 5000;
## Delete-Query
## ☘️ DELETE
- `A delete query is used in SQL to remove records from a table based on specified conditions.`
- `Please be careful when using delete queries, especially without a WHERE clause, as it can result in the removal of all records from the specified table. `
🔥 Syntax:
DELETE FROM table_name
WHERE condition;
👀 Example:
DELETE FROM employees
WHERE salary < 30000;
## Primary-And-Foreign-Key
## ☘️ PRIMARY KEY
- `A primary key is a unique identifier for a record in a database table.`
- `It must contain unique values and cannot have NULL values.`
- `Each table in a relational database typically has a primary key that uniquely identifies each record in that table.`
- `The primary key is used to establish relationships between tables.`
👀 Example
CREATE TABLE cities
(
city_id INT PRIMARY KEY,
city_name VARCHAR(50),
country VARCHAR(50)
);
INSERT INTO cities (city_id, city_name, country)
VALUES
(1, 'New York', 'USA'),
(2, 'London', 'UK'),
(3, 'Tokyo', 'Japan'),
(4, 'Paris', 'France');
## ☘️ FOREIGN KEY:
- `A foreign key is a field in a database table that is a primary key in another table.`
- `It establishes a link between the data in two tables.`
- `The foreign key in one table points to the primary key in another table.`
- `It is used to maintain referential integrity between the two related tables.`
👀 Example
CREATE TABLE students
(
student_id INT PRIMARY KEY,
student_name VARCHAR(50),
age INT,
city_id INT,
FOREIGN KEY (city_id) REFERENCES cities(city_id)
);
INSERT INTO students (student_id, student_name, age, city_id)
VALUES
(101, 'John Doe', 20, 1),
(102, 'Jane Smith', 22, 2),
(103, 'Ken Yamada', 21, 3),
(104, 'Emma Johnson', 23, 4);
## Joins
## ☘️ Join Query
`Joins are operations that combine rows from two or more tables based on a related column between them. The purpose of joins is to retrieve data from multiple tables in a single result set.`
**1. Inner Join:**
- Returns only the rows where there is a match in both tables based on the specified condition.
🔥 Syntax
SELECT *
FROM table1
INNER JOIN table2 ON table1.column = table2.column;
👀 Example
SELECT *
FROM students
INNER JOIN cities ON students.city_id = cities.city_id;
**2. Left Join (or Left Outer Join):**
- Returns all rows from the left table (`students`) and the matched rows from the right table (`cities`). If there is no match, NULL values are returned for columns from the right table.
🔥 Syntax
SELECT *
FROM table1
LEFT JOIN table2 ON table1.column = table2.column;
👀 Example
SELECT *
FROM students
LEFT JOIN cities ON students.city_id = cities.city_id;
**3. Right Join (or Right Outer Join):**
- Returns all rows from the right table (`cities`) and the matched rows from the left table (`students`). If there is no match, NULL values are returned for columns from the left table.
🔥 Syntax:
SELECT *
FROM table1
RIGHT JOIN table2 ON table1.column = table2.column;
👀 Example
SELECT *
FROM students
RIGHT JOIN cities ON students.city_id = cities.city_id;
**4. Cross Join:**
- Returns the Cartesian product of both tables, meaning every row from the left table is combined with every row from the right table.
🔥 Syntax:
SELECT *
FROM table1
CROSS JOIN table2;
👀 Example
SELECT *
FROM students
CROSS JOIN cities;
## Sub-Query
# ☘️ Sub Query
`A subquery, also known as an inner query or nested query, is a query within another SQL query. Subqueries are enclosed in parentheses and can be used in various parts of a SQL statement, such as the SELECT, FROM, WHERE, and HAVING clauses.`
🔥 Syntax
SELECT column_name
FROM table_name
WHERE
(SELECT column_name FROM table_name)
👀 Example
SELECT student_name
FROM students
WHERE age > (SELECT AVG(age) FROM students);
## Exists-And-Not-Exists
## ☘️ EXISTS:
`The EXISTS operator is used to check if a subquery returns any rows. If the subquery returns at least one row, the condition is considered to be true, and the outer query continues.`
🔥 Syntax:
SELECT column_name
FROM table1
WHERE EXISTS
(SELECT column_name FROM table_name2);
👀 Example:
SELECT name
FROM students
WHERE EXISTS
(SELECT id FROM cities WHERE name = 'London');
## ☘️ NOT EXISTS:
`The NOT EXISTS operator is the opposite of EXISTS. It is used to check if a subquery returns no rows. If the subquery returns no rows, the condition is considered to be true, and the outer query continues.`
🔥 Syntax
SELECT column_name
FROM table1
WHERE NOT EXISTS
(SELECT column_name FROM table_name2);
👀 Example
SELECT name
FROM students
WHERE NOT EXISTS
(SELECT id FROM cities WHERE name = 'London');