| Statement | What it does | Example |
|---|---|---|
| SELECT | Retrieves data from a database | SELECT * FROM users; |
| SELECT DISTINCT | Returns unique values | SELECT DISTINCT city FROM users; |
| SELECT ... AS | Aliases a column | SELECT name AS full_name FROM users; |
| Statement | What it does | Example |
|---|---|---|
| WHERE | Filters records | SELECT * FROM users WHERE age > 18; |
| LIKE | Searches for a specified pattern in a column | SELECT * FROM users WHERE name LIKE 'J%'; |
| IN | Checks if a value exists in a list | SELECT * FROM users WHERE city IN ('New York', 'Los Angeles'); |
| Statement | What it does | Example |
|---|---|---|
| INNER JOIN | Returns records that have matching values in both tables | SELECT users.name, orders.order_id FROM users INNER JOIN orders ON users.id = orders.user_id; |
| LEFT JOIN | Returns all records from the left table, and the matched records from the right table | SELECT users.name, orders.order_id FROM users LEFT JOIN orders ON users.id = orders.user_id; |
| RIGHT JOIN | Returns all records from the right table, and the matched records from the left table | SELECT users.name, orders.order_id FROM users RIGHT JOIN orders ON users.id = orders.user_id; |
| Statement | What it does | Example |
|---|---|---|
| COUNT | Returns the number of rows | SELECT COUNT(*) FROM users; |
| SUM | Returns the sum of a numeric column | SELECT SUM(salary) FROM users; |
| AVG | Returns the average value of a numeric column | SELECT AVG(salary) FROM users; |
| Statement | What it does | Example |
|---|---|---|
| INSERT INTO | Inserts new records into a table | INSERT INTO users (name, age) VALUES ('John', 30); |
| UPDATE | Updates existing records in a table | UPDATE users SET age = 31 WHERE name = 'John'; |
| DELETE | Deletes records from a table | DELETE FROM users WHERE name = 'John'; |
| Statement | What it does | Example |
|---|---|---|
| CREATE TABLE | Creates a new table | CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(255), age INT); |
| ALTER TABLE | Modifies an existing table | ALTER TABLE users ADD COLUMN email VARCHAR(255); |
| DROP TABLE | Deletes a table | DROP TABLE users; |
| Statement | What it does | Example |
|---|---|---|
| PRIMARY KEY | Uniquely identifies each record in a table | CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(255), age INT); |
| FOREIGN KEY | Links two tables together | CREATE TABLE orders (id INT PRIMARY KEY, user_id INT, product_id INT, FOREIGN KEY (user_id) REFERENCES users(id)); |
| UNIQUE | Ensures that all values in a column are unique | CREATE TABLE users (id INT PRIMARY KEY, email VARCHAR(255) UNIQUE, name VARCHAR(255)); |