(i) DDL - Data Definition Language
(ii) DML - Data Manipulation Language
(iii) DCL - Data Control Language
(iv) TCL - Transaction Control Language
(v) DQL - Data Query Language

One of the most important tasks when working with SQL is to generate Queries and retrieve data. A Query is a command given to get a desired result from the database table. The SELECT command is used to query or retrieve data from a table in the database. It is used to retrieve a subset of records from one or more tables. The SELECT command can be used in various forms:
Syntax of SELECT command:
SELECT < column-list > FROM < table-name > ;
(i) Table-name is the name of the table from which the information is retrieved.
(ii) Column-list includes one or more columns from which data is retrieved.

The SQL provides a predetermined set of commands to work on databases.

(i) INSERT:
INSERT INTO <table-name>
[column-list] VALUES (values);
(ii) DELETE:
DELETE FROM table-name WHERE condition;
(iii) UPDATE:
UPDATE <table-name > SET column-name = value, column-name = value, ... WHERE condition;

(i) It should identify the type of data division such as data item, segment, record and database file.
(ii) It gives a unique name to each data item type, record type, file type and data base.
(iii) It should specify the proper data type.
(iv) It should define the size of the data item.
(v) It may define the range of values that a data item may use.
(vi) It may specify privacy locks for preventing unauthorized data entry.