Chapter 6, Problem 11RQ

Program Plan Intro

SQL:

• SQL stands for “Structured Query Language”.
• The current version of SQL is “ANSI SQL – 92”.
• SQL is not a programming language. It is text-based and it is also called as data sublanguage.
  • In order to get SQL as a complete programming language, it should be included in scripting languages like Java, C#, and so on.
• It contains constructs which are used to define and process database. They are executed using DBMS-supplied command prompt.
• Some of the DBMS products provide GUI tools in order to perform tasks are as follows:
  • SQL Server
  • Oracle Database
  • MySQL

Data Definition Language (DDL):

• It is used for creating tables and other structures. They perform operations like, creating tables, modifying database, and removing database.

ALTER TABLE Statement:

• “ALTER TABLE” statement comes under Data Definition Language.
• It is used to modify column, add constraints, add column(s), drop column, rename column name and table name, drop constraints, and so on.

Syntax:

The Syntax to drop constraint is as follows:

ALTER TABLE table_Name ADD CONSTRAINT constraintName;

Query to alter the table:

ALTER TABLE EMP_1 ADD PROJ_NUM CHAR(3);

Explanation:

• The above query add “PROJ_NUM” to the table “EMP_1”.
• The “PROJ_NUM” is declared as “CHAR” datatype.