Introduction To SQL And SQL Commands

In this article, I am going to explain different types of SQL commands which are DDL, DML, DQL, DCL, and TCL.

SQL

 
SQL stands for Structured Query Language. SQL is used to create, remove, alter the database and database objects in a database management system and to store, retrieve, update the data in a database. SQL is a standard language for creating, accessing, manipulating database management system. SQL works for all modern relational database management systems, like SQL Server, Oracle, MySQL, etc.
 

Different types of SQL commands

 
SQL commands can be categorized into five categories based on their functionality.
 
DDL
 
DDL stands for data definition language. DDL commands are used for creating and altering the database and database object in the relational database management system, like CREATE DATABASE, CREATE TABLE, ALTER TABLE, etc. The most used DDL commands are CREATE, DROP, ALTER, and TRUNCATE.
  • CREATE
    CREATE command is used to create a database and database object like a table, index, view, trigger, stored procedure, etc.

    Syntax
    CREATE TABLE Employee (Id INT, Name VARHCAR (50), Address VARCHAR (100));

  • ALTER
    ALTER command is used to restructure the database object and the settings in the database.

    Syntax
    ALTER TABLE Employee ADD Salary INT;

  • TRUNCATE
    TRUNCATE command is used to remove all the data from the table. TRUNCATE command empties a table.

    Syntax
    TRUNCATE TABLE Employee;

  • DROP
    DROP command is used to remove the database and database object.

    Syntax
    DROP TABLE Employee;
DML
 
DML stands for data manipulation language. DML commands are used for manipulating data in a relational database management system. DML commands are used for adding, removing, updating data in the database system, like INSERT INTO TableName, DELETE FROM TableName, UPDATE tableName set data, etc. The most used DML commands are INSERT INTO, DELETE FROM, UPDATE.
  • INSERT INTO
    INSERT INTO command is used to add data in the database table.

    Syntax
    INSERT INTO Employee (Id, Name, Address, Salary) VALUES (1, ‘Arvind Singh’, ‘Pune’, 1000);

  • UPDATE
    UPDATE command is used to update data in the database table. A condition can be added using the WHERE clause to update a specific row.

    Syntax
    UPDATE Employee SET Address = ‘Pune India’, Salary = 100 WHERE Id =1;

  • DELETE
    DELETE command is used to remove data from the database table. A condition can be added using the WHERE clause to remove a specific row which meets the condition.

    Syntax
    DELETE FROM Employee WHERE Id =1;
DQL
 
DQL stands for data query language. DQL command is used for fetching the data. DQL command is used for selecting data from the table, view, temp table, table variable etc. There is only one command under DQL which is the SELECT command.

Syntax
SELECT * FROM Employee;

DCL
 
DCL stands for data control language. DCL commands are used for providing and taking back the access rights on the database and database objects. DCL command used for controlling user’s access on the data. Most used DCL commands are GRANT and REVOKE.

GRANT
 
GRANT is used to provide access right to user.
 
Syntax
GRANT INSERT, DELETE ON Employee TO user;
 
REVOKE
 
REVOKE command is used to take back access right from the user, it cancels access right of the user from the database object.
 
Syntax
REVOKE ALL ON Employee FROM user;
 
TCL
 
TCL stands for transaction control language. TCL commands are used for handling transactions in the database. Transactions insure data integrity in the multi user environment. TCL commands can rollback and commit data modification in the database. The most used TCL commands are COMMIT, ROLLBACK, SAVEPOINT, and SET TRANSACTION.
 
COMMIT
 
COMMIT command is used to save or apply the modification in the database.
 
ROLLBACK
 
ROLLBACK command is used to undo the modification.
 
SAVEPOINT
 
SAVEPOINT command is used to temporarily save a transaction, the transaction can roll back to this point when it's needed.
 
Syntax
Just write COMMIT or ROLLBACK or SAVEPOINT;