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SQL Types

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Last modified: Jun 22, 2026
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SQL (Structured Query Language) includes multiple command categories for interacting with databases.

Data Control Language (DCL)

  • GRANT
  • REVOKE
  • LOCK TABLE

DCL examples

GRANT SELECT, INSERT ON testdb.* TO 'app_user'@'localhost';
REVOKE INSERT ON testdb.* FROM 'app_user'@'localhost';
LOCK TABLES Persons READ;
UNLOCK TABLES;

Data Definition Language (DDL)

  • CREATE (DATABASE, TABLE, FUNCTION, INDEX, VIEW, PROCEDURE, TRIGGER)
  • ALTER (DATABASE, TABLE, COLUMN, CONSTRAINT)
  • DROP (DATABASE, TABLE, COLUMN, TRIGGER)

Server and DBMS Startup/Configuration

-- Start web server and DBMS through GUI or CLI
 
-- XAMPP on Windows
PS C:\> cd C:\xampp\mysql\bin\
PS C:\> ./mysql -u root -p

CREATE examples

CREATE DATABASE test;
 
CREATE TABLE IF NOT EXISTS Persons (
    ID INT AUTO_INCREMENT,
    Country INT,
    Company INT,
    FirstName VARCHAR(30),
    LastName VARCHAR(30),
    PRIMARY KEY (ID),
    CONSTRAINT FK_Persons_Country FOREIGN KEY (Country) REFERENCES Country(ID),
    CONSTRAINT FK_Persons_Company FOREIGN KEY (Company) REFERENCES Company(ID)
) AUTO_INCREMENT = 1;

ALTER and DROP examples

ALTER DATABASE comp SET DEFAULT CHARACTER SET LATIN9;
 
ALTER TABLE Persons
ADD FOREIGN KEY (Country) REFERENCES Country(ID);
 
DROP DATABASE databasename;
DROP TABLE tablename;
DROP TRIGGER IF EXISTS tr_change_price;

Data Manipulation Language (DML)

  • SELECT
  • INSERT
  • UPDATE
  • DELETE

DML examples

SELECT * FROM Persons;
 
INSERT INTO Persons (Country, Company, FirstName, LastName)
VALUES (1, 2, 'John', 'Doe');
 
UPDATE Persons
SET LastName = 'Smith'
WHERE ID = 1;
 
DELETE FROM Persons
WHERE ID = 1;

Transaction Control Language (TCL)

  • START TRANSACTION
  • COMMIT
  • ROLLBACK
  • SAVEPOINT

TCL examples

START TRANSACTION;
 
UPDATE Persons
SET Company = 3
WHERE ID = 1;
 
SAVEPOINT before_commit;
COMMIT;
 
ROLLBACK;

Useful Commands

  • SHOW
  • USE
  • DESC
  • EXPLAIN
  • DELIMITER

Useful command examples

USE test;
SHOW TABLES;
DESC Persons;
EXPLAIN SELECT * FROM Persons;
DELIMITER //

References