Friday, 1 June 2018

SQL Statements and Rules

SQL command or statement is a special kind of sentence that contains clauses and all end with a semicolon(;) just as a sequence ends with a period.

SQL statements are divided into four sub language:

(i) Data Definition Language (DDL):- It is used to define the structure of tables in the database.It contains the necessary statement to CREATE , RENAME , ALTER and DROP the tables.

(ii) Data Manipulation Language (DML):- It is a used to manipulate the data in the database.It contains statement to UPDATE , DELETE , INSERT and SELECT data that is stored in the database.

(iii)Data Control Language (DCL):- It is used to control data stored in the database.It contains statement give permission to access the data in the database.These statements are GRANT and REVOKE.

(iv) Transaction Control Language(TCL):- It is used to control the transaction in a database system. It contains statements like COMMIT , ROLLBACK and SAVEPOINT.

Rules for SQL Command/Statements

Rules for SQL commands are given below:
* SQL statements are not case sensitive.
* SQL statements can be executed on one or more tables.
* Keywords cannot be abbreviated.
* The statement can be typed in single line or multiple lines.
* Place a semicolon at the end of the SQL statements.
* A comma (,) is used to separate parameters without a clause.
* Characters and data constants or literals must be enclosed in single quotes(' ').

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