SQL | Commands

SQL Commands

SQL can perform wide range of operations using its commands such as INSERT, UPDATE,

DELETE, and lot more. The commands are classified to groups according to their usage.

Types of SQL Commands

Data Definition Language (DDL)
Data Manipulation Language (DML)
Data Control Language (DCL)
Transaction Control Language (TCL)

1. Data Definition Language (DDL)

Data definition language is use to create or define a new data or table in a database. we can also redefine or rename and modify a new data using DDL commands.

Title	Explanation
Create	Create Command is use to create a new table or database for the first time.
Alter	Alter is use to change and modify the existing table or column with new features.
Drop	Drop is use to drop and delete an entire table or database along with his structure and you can't rollback to previous state once you drop the table. It is slower than Truncate.
Rename	Rename is use to rename the table, objects or database.
Truncate	Truncate works similar to drop command with only difference is that the structure of the table is not deleted only the values are deleted and it is faster than drop statement.

2. Data Manipulation Language (DML)

Data manipulation language is use to manipulate and make changes in a existing data.

Title	Explanation
Select	Select command is use to fetch and retrieve the desired records from the table. It is going to be most frequently used command in our course.
Insert	Insert command is use to insert the new values to an existing tables.
Update	Update is use to modify and update the existing records.
Delete	Delete is use to delete a specific record or a complete record. The main difference between delete and truncate is that in delete we can use the where clause to specify the condition.

3. Data Control Language (DCL)

Data control language is use to grant and revoke permissions from users to access and manipulate database.

Command	Explanation
GRANT	Grant is use to grant a new access permission to a user.
REVOKE	revoke is use to revoke the permissions user already have.

4. Transaction Control Language (TCL)

Transaction control language is use to save the changes permanently to the database or undo the changes.

Command	Explanation
COMMIT	It is use to make the changes permanently saved to the database.
ROLLBACK	It helps us to do undo the changes we made. It is advisable to use the rollback command carefully because it will take us to the last uncommited state.