SQL Commands

SQL Commands

Data Definition Language(DDL)

  • DDL deals with the structure of objects.
  • DDL commands interact with database directly.
  • DDL commands enforce an implement commit before & after statement .
  • Cannot undo (rollback) the changes.
  • DDL commands are faster (performance).

Here are some commands that come under DDL:

  • CREATE 
  • RENAME
  • ALTER
  • TRUNCATE
  • DROP

1.CREATE  

This command is used to create database objects,  such as table ,views etc.

Syntax

CREATE TABLE

( column1 datatype(size), column2 datatype(size), …….. );

Example

CREATE TABLE student_details( student_name varchar2(20),student_rollnum number(10));

 

2.ALTER

This command is used to modify the structure of a table

  • ALTER-Modify
  • ALTER-ADD
  • ALTER-Rename
  • ALTER-DROP
  1. ALTER-Modify

This command is used to increase or decrease the size of datatype and also we can change the datatype from old datatype to new datatype.

Syntax :-

ALTER  TABLE  

MODIFY (

 Column1  datatype(size),

Column2  datatype(size),

…….

ColumnN  datatype(size),

);

ii.ALTER-ADD

This command is used to ADD the new column to the existing table.

Syntax

ALTER TABLE

ADD  NEW_COLUMN_NAME  DATATYPE(SIZE);

Example

ALTER  TABLE  students_details

                ADD roll_num number(8);

iii. ALTER-Rename

                This command is used to change column name from old column name to new column name.

Syntax

ALTER TABLE

                                RENAME COLUMN  old_column_name TO new_column_name;

 

Note

                We can’t change more than one column at time.

 

iv. ALTER-DROP

                This command is used to drop the column from the existing table.

syntax

ALTER TABLE

                DROP COLUMN column_name;

EXAMPLE

ALTER TABLE student_details

                DROP COLUMN roll_num;

3.RENAME

This command is used to change table name from old table name to new table name.

Syntax

RENAME old_table_name TO new_table_name;

Example

RENAME table1 TO table2;

4.TRUNCATE

This is used to truncate (delete) all the records from existing table.

Syntax

 TRUNCATE TABLE  ;

5.DROP

                This command is used to drop the table from the database.

Syntax

                DROP TBALE  ;

 

 

vhjgfjhgku

NextPage IT Solutions, imperatively focus on development, optimization, and promotion of web-based products and applications. We thrive on delivering intuitive …
 
 
Pages: 1 2

Leave a Reply