Types of commands in Structured Query Language (SQL):
Data Definition Language (DDL): Create, Alter, Drop, Truncate, Rename
Data Retrieval Language (DRL): Select
Data Manipulation Language (DML): Insert, Delete and Update
Data Control Language (DCL): Grant and Revoke
Transaction Control Language (TCL): Commit, Save point and Rollback
Create Table Command:
This command allows you to create a table.
Syntax: CREATE TABLE table_name (Column1 data type null/notnull,column2 data type null/not null..);
Each and every column should have a data type.
Creating a table from an existing table:
Syntax: create table table_name as (select * from existing table_name);
Creating a table from the selected columns of an existing table:
Syntax: create table table_name as (select column1,column2 from existing table_name);
Creating a table definition without the data:
Syntax: create table table_name as (select * from existing table_name where 1=2);
Alter Table Command:
Alter table command allows you to add, delete and modify the columns in an existing table.
To add a column:
Syntax: alter table table_name add column1 data type;
To modify a column:
Syntax: alter table table_name modify column1 data type;
To delete a column:
Syntax: alter table table_name drop column1;
Drop Command:
The DROP command removes a table from the database. All the tables' rows, indexes and privileges will also be removed.
Syntax: Drop table table_name
Truncate Command:
Truncate is used to delete all the rows from the table and free the space containing the table.
Syntax: truncate table table_name
Rename Command:
This is used to rename an existing table.
Syntax: rename old_table_name to new_table_name
