Data Defination Language(DDL )

Data Definition Language:

1 Create
2 Alter
3 Drop
4 Truncate

Create : To create the data definition.
Syntax
Create database < Database_Name >
Example 
Create database Customers

Syntax for creating a Table:
            -CREATE TABLE <table_name>(
             column_name1 <dtype> [width],
             column_name1 <dtype> [width],
             ………………….
             column_namen <dtype> [width])

-Table names must be unique within the database.
-Column names must be unique within the table.
-Every table can have maximum of 1024 and minimum of 1 column.
The table name should start with alphabet.
Spaces and Special Symbols are not allowed.
The table name can contain max of 128 characters.

Alter:
It is used to modify the structure of the table

Using Modify Command  to do the following things
1 Adding New Column
2 Drop Column
3 Modifying Column(increment, decrement  field Size),(changing data type)

1 Adding New Column

Syntax:

Alter table <table name> Add <Col Name> datatype[size]

Example: Alter table students Add rollno int


2 Syntax to Drop the Column
Alter Table <Table Name> Drop column <Column Name>

Example: Alter table student Drop column studentid

3 Modifying Columns

Syntax:
 Inserting the Width of the Column
Alter table <TableName> Alter Column ColName datatype

Example : Alter table <TableName> Alter Column ColName datatype
      

Changing the DataType of the Column
Alter table <TableName> Alter Column ColName datatype(size)
Example : Alter table Students Alter column sname varchar(20)

Drop Command: If we want to destroy the existing tables present in the database we use the Drop Command.

Syntax: DROP TABLE <TableName>

Example : Drop Table Customers
Truncate Command: Removes all rows from a table. Here the columns Remains the same so that you can add New Records in the table.

Note: We do not have Where Clause Here.

Syntax: TRUNCATE TABLE  <TableName>

Example : TRUNCATE TABLE Customers

 Truncate 

·         Truncate table is faster in execution. 
·         Truncate Releases Memory
·         It will Reset Identity
·         It Deletes all the records

Delete 

·         Delete table is slower in execution. 
·         Delete will not  Releases Memory
·         It will Not Reset Identity
·         It deletes all the records or Particular Record.