Understanding SQL in MySQL: From DDL to DCL

 

📦 MySQL is a widely-used relational database management system (RDBMS) that uses Structured Query Language (SQL) to manage and manipulate data. SQL is divided into several categories, each serving a specific purpose: DDL, DML, DQL, TCL, and DCL.

1. Data Definition Language (DDL)

DDL commands are used to define and manage database structures such as tables, indexes, and schemas. The main DDL commands include CREATE, ALTER, DROP, and TRUNCATE.

⭐ CREATE: This command creates a new database object.

CREATE TABLE students (

id INT PRIMARY KEY,

name VARCHAR(100),

age INT

);

⭐ ALTER: This command modifies an existing database object.

ALTER TABLE students ADD COLUMN email VARCHAR(100);

⭐ DROP: This command deletes an existing database object.

DROP TABLE students;

⭐ TRUNCATE: This command removes all records from a table without deleting the table itself.

TRUNCATE TABLE students;

2. Data Manipulation Language (DML)

DML commands are used to manipulate data within database objects. The primary DML commands are INSERT, UPDATE, and DELETE.

⭐ INSERT: This command adds new records to a table.

INSERT INTO students (id, name, age) VALUES (1, 'John Doe', 20);

⭐ UPDATE: This command modifies existing records in a table.

UPDATE students SET age = 21 WHERE id = 1;

⭐ DELETE: This command removes records from a table.

DELETE FROM students WHERE id = 1;

3. Data Query Language (DQL)

DQL is primarily used to query and retrieve data from databases. The main DQL command is SELECT.

⭐ SELECT: This command retrieves records from one or more tables.

SELECT * FROM students;

4. Transaction Control Language (TCL)

TCL commands manage transactions within a database to ensure data integrity. The primary TCL commands are COMMIT, ROLLBACK, and SAVEPOINT.

⭐ COMMIT: This command saves all changes made during the current transaction.

COMMIT;

⭐ ROLLBACK: This command undoes changes made during the current transaction.

ROLLBACK;

⭐ SAVEPOINT: This command sets a point within a transaction to which you can later roll back.

SAVEPOINT savepoint1;

5. Data Control Language (DCL)

• DCL commands manage access permissions to the database. The main DCL commands are GRANT and REVOKE.

⭐ GRANT: This command gives specific privileges to users.

GRANT SELECT, INSERT ON students TO 'username';

⭐ REVOKE: This command removes specific privileges from users.

REVOKE SELECT, INSERT ON students FROM 'username';