Common SQL commands¶

Data Manipulation Language (DML)¶

DML commands manage data within database tables.

Common DML commands include:

SELECT: This command retrieves data from one or more tables in the database.
```
mysql> SELECT * FROM customers;
```

INSERT: This command adds new records to a table.

mysql> INSERT INTO customers (name, email) VALUES ('John Doe', 'john@example.com');

UPDATE: This command modifies existing records in a table.

mysql> UPDATE customers SET email = 'newemail@example.com' WHERE id = 1;

DELETE: This command removes records from a table.
```
mysql> DELETE FROM customers WHERE id = 1;
```

Data Definition Language (DDL)¶

DDL commands define, modify, and remove database objects such as tables, indexes, and views.

Common DDL commands include:

CREATE: This command creates new database objects like tables, indexes, and views.
```
mysql> CREATE TABLE employees (id INT, name VARCHAR(50));
```
ALTER: This command modifies the structure of existing database objects.
```
mysql> ALTER TABLE employees ADD COLUMN email VARCHAR(100);
```
DROP: This command removes database objects from the database.
```
mysql> DROP TABLE employees;
```

Data Control Language (DCL)¶

DCL commands control access to database objects and define privileges.

Common DCL commands include:

GRANT: This command grants specific privileges to database users.

mysql> GRANT SELECT, INSERT ON employees TO 'user1'@'localhost';

REVOKE: This command revokes privileges from database users.

mysql> REVOKE INSERT ON employees FROM 'user2'@'localhost';

Transaction Control Language (TCL)¶

TCL commands manage transactions within a database.

Common TCL commands include:

COMMIT: This command saves changes made during the current transaction to the database.
```
mysql> COMMIT;
```
ROLLBACK: This command undoes changes made during the current transaction and restores the database to its previous state.
```
mysql> ROLLBACK;
```

Fundamental SQL links:

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Last update: 2024-08-28