Introduction to SQL

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School:Computer Science -> Topic:Databases -> Topic:SQL

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What is SQL?[edit]

SQL is an acronym for Structured Query Language used for managing databases. This unit introduces SQL concepts in terms of structure, client/server relationships, access control, language elements (syntax and semantics) and other common aspects.

There are mainly 3 kinds of statements in SQL:

  1. DDL (Data Definition Language)
  2. DML (Data Manipulation Language)
  3. DCL (Data Control Language)

SQL commands such as CREATE, ALTER & DROP are DDL commands. SQL commands such as INSERT, DELETE & UPDATE are DML commands. GRANT & REVOKE are DCL commands.

Note: All DDL statements are autocommitted; i.e. the user need not perform any commit after executing DDL statements. DML statements do not commit automatically.

For example: TRUNCATE is a DDL statement whereas DELETE is a DML statement.

TRUNCATE commits automatically.
DELETE does not commit automatically.

SQL was adopted as a standard by ANSI (American National Standards Institute) in 1986 and ISO (International Organization for Standardization) in 1987. This lesson is designed as a prerequisite for product-specific courses that cover the three principal client/server products:

Learners interested in SQL should participate at Topic:Databases and might also consider Topic:Object-relational databases.

Language basics[edit]

under construction - instructors needed