https://github.com/shuvoprogram/postgres_cheatsheet
Master PostgreSQL with this concise cheatsheet! Discover essential commands for database creation, querying, data manipulation, and user management. Level up your SQL skills and manage databases efficiently. Your one-stop reference for PostgreSQL success. #PostgreSQL #DatabaseManagement
https://github.com/shuvoprogram/postgres_cheatsheet
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Master PostgreSQL with this concise cheatsheet! Discover essential commands for database creation, querying, data manipulation, and user management. Level up your SQL skills and manage databases efficiently. Your one-stop reference for PostgreSQL success. #PostgreSQL #DatabaseManagement
- Host: GitHub
- URL: https://github.com/shuvoprogram/postgres_cheatsheet
- Owner: ShuvoProgram
- Created: 2023-08-24T15:07:18.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2023-08-26T17:41:00.000Z (over 2 years ago)
- Last Synced: 2025-02-15T03:29:33.960Z (11 months ago)
- Topics: postgresql
- Homepage:
- Size: 6.84 KB
- Stars: 0
- Watchers: 1
- Forks: 1
- Open Issues: 0
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Metadata Files:
- Readme: readme.md
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README
# PostgreSQL Database Management Commands
This repository contains a collection of PostgreSQL commands for various database management tasks.
## Introduction
This repository provides a set of PostgreSQL commands and examples for managing databases, tables, and data. Each section covers a specific aspect of database management, and the commands are presented with explanations for better understanding.
## Grant Permissions
Grant the necessary permissions to users for performing specific actions within the database.
- **Grant the "CONNECT" permission to the "test" database for the "postgres" user:**
```sql
GRANT CONNECT ON DATABASE test TO postgres;
- **Grant the permission to create databases to the "postgres" user:**
```sql
ALTER USER postgres CREATEDB;
## Database Operations
- **Create a new database named "test2":**
```sql
CREATE DATABASE test2;
- **Rename the database "test2" to "test3":**
```sql
ALTER DATABASE test2 RENAME TO test3;
- **Delete the "test3" database:**
```sql
DROP DATABASE test3;
## Table Operations
- **Create a "student" table with columns for student information:**
```sql
CREATE TABLE student (
student_id INT,
first_name VARCHAR(15),
last_name VARCHAR(15),
cgpa NUMERIC(1, 2) );
- **Rename the "student" table to "learner":**
```sql
ALTER TABLE student RENAME TO learner;
- **Delete the "learner" table:**
```sql
DROP TABLE learner;
## Table Operations
- **Create a "users" table with columns for user information and constraints:**
```sql
CREATE TABLE users (
user_id SERIAL PRIMARY KEY,
username VARCHAR(50) NOT NULL,
email VARCHAR(50) NOT NULL,
age INT DEFAULT 18,
UNIQUE(username, email));
- **Remove all data from the "users" table while keeping its structure:**
```sql
TRUNCATE TABLE users;
- **Insert user data into the "users" table using various methods:**
- **Method 1:**
```sql
INSERT INTO users(user_id, username, email, age)
VALUES ('sam', 'sam@gmail.com', 21);
- **Method 2:**
```sql
INSERT INTO users(username, email, age)
VALUES ('clark', 'clark@gmail.com', 35),
('clark2', 'clark2@gmail.com', 35);
- **Method 3:**
```sql
INSERT INTO users
VALUES (1, 'persian', 'persian@gmail.com'),
(2, 'persian2', 'persian2@gmail.com');
- **Add a "password" column to the "users" table with a default value:**
```sql
ALTER TABLE users
ADD COLUMN password VARCHAR(255) DEFAULT 'admin123' NOT NULL;
- **Delete the "age" column from the "users" table:**
```sql
ALTER TABLE users DROP COLUMN age;
- **Add and modify columns in the "users" table:**
```sql
ALTER TABLE users ADD COLUMN demo INT;
ALTER TABLE users ALTER COLUMN demo TYPE TEXT;
ALTER TABLE users ALTER COLUMN country SET DEFAULT 'bangladesh';
ALTER TABLE users ALTER COLUMN demo DROP DEFAULT;
- **Insert a user with specific values into the "users" table:**
```sql
INSERT INTO users VALUES(4, 'john1', 'john1@gmail.com');
- **Rename the "demo" column to "country" in the "users" table:**
```sql
ALTER TABLE users RENAME COLUMN demo TO country;
ALTER TABLE users ALTER COLUMN country SET NOT NULL;
- **Drop the "NOT NULL" constraint from the "country" column:**
```sql
ALTER TABLE users ALTER COLUMN country DROP NOT NULL;
- **Add a unique constraint to the "email" column in the "users" table:**
```sql
ALTER TABLE users ADD CONSTRAINT unique_email UNIQUE(email);
- **Delete the unique constraint from the "email" column in the "users" table:**
```sql
ALTER TABLE users DROP CONSTRAINT unique_email;
## Retrieving Data
- **Retrieve all data from the "users" table:**
```sql
SELECT * FROM users;
## Foreign Keys Constraint And Data Integrity
- **Create a table named "Employees" to store employee information.:**
```sql
CREATE TABLE Employees (
empID SERIAL PRIMARY KEY,
empName VARCHAR(50) NOT NULL,
departmentID INT,
CONSTRAINT fk_constraint_dept FOREIGN KEY (departmentID) REFERENCES Department(deptID)
);
Explanation: Create a table to store employee details with a foreign key constraint.
- **Retrieve Specific table column:**
```sql
SELECT empid, name, email, joining_date, salary, from employees;
SELECT *
FROM employees
WHERE
name <> 'Eve'
AND salary > 9000
OR name = 'Greta'
- **Update Course Data:**
```sql
UPDATE courses
SET
course_name = 'laravel',
description = 'super'
WHERE course_id = 1;
Explanation: Update course data where course_id is 1.
- **Update Multiple Course Data:**
```sql
UPDATE courses
SET
course_name = 'laravel',
description = 'super'
WHERE course_id > 1;
Explanation: Update course data for courses with course_id greater than 1.
- **Delete Course Data:**
```sql
DELETE FROM courses WHERE course_id = 1;
Explanation: Delete course data where course_id is 1.
## Employees Table (Continued)
- **Create Employees Table (Conditional):**
```sql
CREATE TABLE IF NOT EXISTS employees (
empID SERIAL PRIMARY KEY,
name text NOT NULL,
email TEXT NOT NULL,
salary INT not NULL,
joining_data DATE NOT NULL,
deptID INT NOT NULL,
CONSTRAINT fk_deptID FOREIGN KEY (deptID) REFERENCES department(deptID));
Explanation: Create employees table if it doesn't exist.
- **Select Specific Columns from Employees Table:**
```sql
SELECT empid, name, email, joining_date, salary FROM employees;
Explanation: Retrieve specific columns from the employees table.
- **Filtering Rows with Conditions:**
```sql
SELECT * FROM employees WHERE name LIKE '_r%';
SELECT * FROM employees WHERE name LIKE '__r__';
SELECT * FROM employees WHERE name LIKE 'G%a';
SELECT * FROM employees WHERE deptid IS NULL;
Explanation: Retrieve rows based on specified conditions.
- **Sorting and Limiting Results:**
```sql
SELECT * FROM employees ORDER BY name ASC LIMIT 10 OFFSET 2;
Explanation: Retrieve sorted and limited rows from employees table.
- **Retrieving Maximum Salary:**
```sql
SELECT * FROM employees ORDER BY salary DESC LIMIT 1;
Explanation: Retrieve employee with the highest salary.
- **IN, NOT IN, BETWEEN, and LIKE Operators:**
```sql
SELECT * FROM employees WHERE empid NOT IN (2, 3, 5);
SELECT * FROM employees WHERE salary BETWEEN 10000 AND 15000;
SELECT * FROM employees WHERE name LIKE 'A%';
Explanation: Retrieve rows based on various filtering conditions.
## Joining Tables
- **Inner Join with Explanation:**
```sql
SELECT *
FROM employees
INNER JOIN department ON employees.deptid = department.deptid;
Explanation: Retrieve all columns from both tables where the department ID matches in both tables.
- **Left Join:**
```sql
SELECT *
FROM employees
LEFT JOIN department ON department.department_id = employees.department_id;
Explanation: Retrieve all rows from the left table and matching rows from the right table.
- **Right Join:**
```sql
SELECT *
FROM employees
RIGHT JOIN department ON department.department_id = employees.department_id;
Explanation: Retrieve all rows from the right table and matching rows from the left table.
- **Full Outer Join:**
```sql
SELECT *
FROM employees
FULL JOIN department ON department.department_id = employees.department_id;
Explanation: Retrieve all rows when there is a match in either the left or right table.
- **Cross Join:**
```sql
SELECT * FROM employees CROSS JOIN department;
Explanation: Generate all possible combinations of rows between two tables.
## Aggregate Functions
Perform calculations on groups of rows and summarize data
- **Aggregate Functions with Explanation:**
```sql
SELECT
d.name,
AVG(e.salary),
SUM(e.salary),
MAX(e.salary)
FROM employees e
FULL JOIN department d ON e.dept = d.dept
GROUP BY d.name
HAVING AVG(e.salary) > 60000;
Explanation: Calculate average, sum, and maximum salary for each department, filtering results using the HAVING clause.
- **Aggregate Functions with GROUP BY:**
```sql
SELECT
d.name,
SUM(salary),
AVG(salary),
MIN(salary),
COUNT(*)
FROM department d
FULL JOIN employees e ON e.dept = d.deptid
GROUP BY d.deptid;
Explanation: Group and aggregate salary data by department, calculating sum, average, minimum, and count.
## Subqueries
Use subqueries to perform complex queries within other queries
- **Aggregate Functions with GROUP BY:**
```sql
SELECT
film_id,
title,
rental_rate
FROM film
WHERE rental_rate > 2.98;
Explanation: Retrieve film details where the rental rate is greater than 2.98.