types and details of SQL Statements

SQL provides set of commands for a variety of tasks including the following:

• Querying data
• Updating, inserting and deleting data
• Creating, modifying and deleting database objects
• Controlling access to the database
• Providing for data integrity and consistency.

SQL statements are divided into the following categories

•  
• Data Definition Language(DDL)
• Data Manipulation Language(DML)
• Data Query Language (DQL)
• Data Control Language (DCL)

1) Data Definition Language(DDL)

  This is used to create, alter and delete database objects

  The commands used are create, alter and drop

•   Create table, create view, drop index 
•   Alter table
•   Drop table, drop view, drop index

2) Data Manipulation Language(DML)

  Data manipulation language commands let users insert, modify and delete the data in the database. SQL provides three data manipulation statements insert, update and delete

3) Data Query Language (DQL)

  This is one of the most commonly used SQL statements. This SQL statement enables the users to query one or more tables to get the information they want. SQL has only one data query statement 'select.'

4) Data Control Language (DCL)

  The data control language consists of commands that control the user access to the database objects. Various DCL commands are : Commit, Rollback, Save point, Grant, Revoke.

spP � b p � �� time stamp '2005-04-25 08:25:30.45'

  Dates must be specified in the format-year followed by month followed by day, as shown. The seconds field of time or timestamp can have a fractional part, as in the timestamp above