SQL Cheatsheet

DDL - Data Definition Language

Command	Function	Example
`CREATE TABLE`	Creates a new table	`CREATE TABLE t (id INT PRIMARY KEY);`
`ALTER TABLE`	Modifies table structure	`ALTER TABLE t ADD column VARCHAR(50);`
`DROP TABLE`	Drops a table	`DROP TABLE t;`
`TRUNCATE TABLE`	Removes all data	`TRUNCATE TABLE t;`
`CREATE INDEX`	Creates an index	`CREATE INDEX idx ON t(column);`
`CREATE VIEW`	Creates a view	`CREATE VIEW v AS SELECT * FROM t;`

DML - Data Manipulation Language

Command	Function	Example
`SELECT`	Retrieves data	`SELECT * FROM employee;`
`INSERT INTO`	Adds data	`INSERT INTO t VALUES (1, 'James');`
`UPDATE`	Modifies data	`UPDATE t SET column = 'new';;`
`DELETE`	Deletes data	`DELETE FROM t WHERE id = 1;`
`JOIN`	Combines tables	`SELECT * FROM a JOIN b ON a.id = b.id;`
`GROUP BY`	Groups data	`SELECT dept, COUNT(*) FROM t GROUP BY dept;`
`ORDER BY`	Sorts data	`SELECT * FROM t ORDER BY name ASC;`
`HAVING`	Filters after GROUP BY	`HAVING COUNT(*) > 5`
`UNION`	Combines results	`SELECT * FROM a UNION SELECT * FROM b;`

DCL - Data Control Language

Command	Function	Example
`GRANT`	Grants access rights	`GRANT SELECT ON t TO user1;`
`REVOKE`	Revokes access rights	`REVOKE SELECT ON t FROM user1;`

TCL - Transaction Control Language

Command	Function	Example
`BEGIN TRANSACTION`	Starts a transaction	`BEGIN;`
`COMMIT`	Saves changes	`COMMIT;`
`ROLLBACK`	Reverts changes	`ROLLBACK;`
`SAVEPOINT`	Creates a rollback point	`SAVEPOINT sp1;`

Aggregate Functions

Function	Description
`COUNT()`	Counts the number of rows
`SUM()`	Sums the values
`AVG()`	Average
`MIN()`	Minimum value
`MAX()`	Maximum value

Main Query Structure

SELECT column
FROM table
WHERE condition
GROUP BY column
HAVING condition
ORDER BY column ASC/DESC
LIMIT count;

SQL Execution Order

FROM / JOIN
WHERE
GROUP BY
HAVING
SELECT
DISTINCT
ORDER BY
LIMIT

Important Tips

Always back up before DDL operations in production
Use EXPLAIN to analyze query performance
Indexes speed up SELECT but slow down INSERT/UPDATE
Transactions ensure data integrity
Use aliases for complex queries

Happy Learning, SQL!

You have completed the entire SQL tutorial, from basics to advanced. Keep practicing and applying it in real projects. SQL is an important foundation in application development and data analysis.

Happy learning, and good luck!