DDL Commands in SQL-sql query tool

SQL  DDL Commands

SQL is a Structured Query Language it is the Back End language we have the Front End languages are Java,C#.net,vb.Net,PHP etc and backend languages are MySQL,SQL Server,Oracle etc.All frontend languages are used for writing programming in frontend and backend are used for storing the data in database.In the below you are seen DDL Commands in SQL this Commands are very powerful and useful to all and this are basic steps to learn SQL.

SQL Commands

Data Definition Language:  

These commands are used to create database or database objects like tables,views,triggers,stored procedures,etc.

In DDL we have 4 types of commands they are

1. Alter

2.Create

3.Drop

4.Truncate

*******Alter Command*******

1.Alter

* These commands are used to modify the structure of database or database object.
* By using alter command we can add a new column for the existing table.
* We can remove a column from the table.We can change the datatype of the column.

Syntax:- alter table tablename

Q)Write a query to add a new column for existing table?

Syn:-  alter table tablename add columnname datatype

Ex:- alter table emp add salary money

Q)Write a query to remove salary column from existing table?

Syn:-  alter table tablename drop column  columnname

Ex:-   alter table emp drop column salary

*******Drop Command*******

2.Drop

It is used to drop the database or database objects like tables.

Syntax for to drop a database

Syn:drop database databasename

Ex:-  drop database employee

Syntax for drop a table

Syn:   drop table tablename

Ex:-   drop table emp

*******Create Command*******

3.Create

By using this command we can create tables or databases. 

Syntax for create table

Syn:  create table tablename

Ex:- create table emp

Syntax for create database

Syn:   create database Databasename

Ex:-  create database employee 

*******Truncate Command*******

4.Truncate

Truncate will delete the table data but not the table structure.
Syntax for truncate the table

 Syn: truncate table tablename

Ex:- truncate table emp

 Q)What is the difference between drop and truncate?

Truncate will delete the table data but not the table structure.
Drop will delete the table data along with table structure.
We can insert the record in the table even though we can truncate the table.
We can not insert the record in the table once the table is Droped.

In this article you can find the detail description about DDL commands that commands will help you to prepare for the interviews.These topic is very important and easy topic and it is the most frequently asking topic in interview purpose.

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