DDL Full Form

DDL stands for Data Defination Language.
These commands are used to change the structure of a database and database objects.For example, DDL commands can be used to add, remove, or modify tables with in a database.

The DDL commands are:

1. CREATE
2. ALTER
3. DROP
4. TRUNCATE
5. RENAME

1. CREATE :
This command is used to create table in the relational database .
This can be done by specifying the names and datatypes of various columns.

Syntax:

CREATE TABLE TABLE_NAME
(
    column_name1 datatype1,
    column_name2 datatype2,
    column_name3 datatype3,
    column_name4 datatype4
);

The column_name in create table command will tell the name of the column and corresponding datatype will specify the datatype of that column.Here in this table the three column_names namely – Student_id is of type int ,Name is of type varchar and Marks is of type int.
for example:

CREATE TABLE 
Employee
(Student_id INT, 
Name VARCHAR(100), 
Marks INT); 

2. ALTER :
Alter command is used for altering the table in many forms like:

1. Add a column
2. Rename existing column
3. Drop a column
4. Modify the size of the column or change datatype of the column

1. ADD using ALTER –
   Syntax to add column :

   ALTER TABLE table_name ADD(
       column_name datatype); 

   The above command will add a new column to the table.And the resulting table will have one more column like this:

   ALTER TABLE Student 
   ADD
   (Address  VARCHAR(200)); 

   Here this command will add a new column “Address” in the table Student of datatype varchar(200);

   Student_id	Name	Marks	Address

2. RENAME using ALTER –
   Syntax to rename column :

   ALTER TABLE 
   table_name 
   RENAME 
   old_column_name TO new_column_name; 

   The above command will rename the existing column to new column.

   ALTER TABLE 
   Employee 
   RENAME 
   Marks TO Age; 

   The command above will change the column_name from Marks to Age;

   Student_id	Name	Age	Address

3. DROP using ALTER –
   Syntax to Drop a column :

   ALTER TABLE
   table_name
   DROp
   (column_name); 

   The above command will delete the existing column.
   For example:

   ALTER TABLE Employee 
   DROP
   (Age);  

   Here the column_name =”Age”, has been deleted by this command;

   Student_id	Name	Address

4. MODIFY using ALTER –
   Syntax to Modify a column :

   ALTER TABLE
   Employee MODIFY
   (column_name datatype); 

   The above command will modify the existing column .
   For example:

   ALTER TABLE 
   student 
   MODIFY
   (name varchar(300)); 

   The above command will modify the column_name “Name” by changing the size of that column.

   Student_id	Name	Address

3. TRUNCATE :
This command removes all the records from a table. But this command will not destroy the table’s structure.
Syntax :

TRUNCATE TABLE table_name

This will delete all the records from the table.For example the below command will remove all the records from table student.

Example:

TRUNCATE TABLE Student; 

4. DROP :
This command completely removes the table from the database along with the destruction of the table structure.

Syntax –

DROP TABLE table_name

This will delete all the records as well as the structure of the table.
This is the main difference between TRUNCATE AND DROP.-TRUNCATE only removes the records whereas DROP completely destroys the table.

Example:

DROP TABLE Student; 

This command will remove the table records as well as destroys the schema too.

This is all about the DDL commands.

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

shrusty7

Check out this Author's contributed articles.