Sunday, September 12, 2010

SQL Basics

I thought to write few posts about SQL and Database testing. This post is the result of that interest.

SQL - Structured Query Language. SQL is used to interact with databases. SQL is a non-procedural language and has few standards. SQL is standardized by the American National Standards Institute (ANSI).

Rules for writing SQL statements

  • It is not case sensitive.
  • It cannot be abbreviated or split across lines.
  • It can be on one or more lines.
  • Indents are used to enhance readability.
  • Clauses are usually placed on separate lines.

SQL's Components / Sub Languages
SQL consists of few components and given below:
  • DDL - Data Definition Language - Create, Alter, Drop, Truncate - For creating, altering and dropping the database objects like tables, viewes, indexes, synonyms,sequences and contraints.
  • DML - Data Manipulation Language - Insert, Update, Delete - For reading and updating data.
  • DRL - Data Retrieval Language - SELECT - For querying the data. SELECT has many clauses.
  • TCL - Transaction Control Language - Commit, Rollback, SavePoint - These allow to group one or more DML statements into units of work or transactions. All statements in a transaction either succeed or fail as a single group.
  • DCL - Data Control Language - Grant, Revoke - For managing database security, by creating user ids and assigning or removing privileges from them.


Sandeep Reddy said...

Aldus Logan said...

Thanks for sharing this information with all. just keep update the blog with useful information.
online business software