Types of SQL Commands

The basic categories of commands used in SQL to perform various functions. These functions include building database objects, manipulating objects, populating database tables with data, updating existing data in tables, deleting data, performing database queries, controlling database access, and overall database administration.

The main categories are

• DDL (Data Definition Language)

• DML(Data Manipulation Language)

• DQL (Data Query Language)

• DCL (Data Control Language)

• Data administration commands

• Transactional control commands

  
  

  Defining Database Structures (DDL)

  Data Definition Language, DDL, is the part of SQL that allows a database user to create and restructure database objects, such as the creation or the deletion of a table.

  The main DDL commands discussed during following hours include the following:

  CREATE TABLE

  ALTER TABLE

  DROP TABLE

  CREATE INDEX

  ALTER INDEX

  DROP INDEX

  
  

  Manipulating Data (DML)

  Data Manipulation Language, DML, is the part of SQL used to manipulate data within objects of a relational database.

  There are three basic DML commands:

  INSERT

  UPDATE

  DELETE

  
  

  Selecting Data (DQL)

  Data Query Language (DQL) is the most concentrated focus of SQL for a relational database user. The command is as follows:

  SELECT

  
  

  
  

  Data Control Language (DCL)

  Data control commands in SQL allow you to control access to data within the database. These DCL commands are normally used to create objects related to user access and also control the distribution of privileges among users. Some data control commands are as follows:

  ALTER PASSWORD

  GRANT

  REVOKE

  CREATE SYNONYM

  
  

  Data Administration Commands

  Data administration commands allow the user to perform audits and perform analyses on operations within the database. They can also be used to help analyze system performance. Two general data administration commands are as follows:

  START AUDIT

  STOP AUDIT

  
  

  Transactional Control Commands

  In addition to the previously introduced categories of commands, there are commands that allow the user to manage database transactions.

  • COMMIT Used to save database transactions

  • ROLLBACK Used to undo database transactions

  • SAVEPOINT Creates points within groups of transactions in which to ROLLBACK

  • SET TRANSACTION Places a name on a transaction