Sql Concepts


Structured Query Language (SQL) is the standard language designed to access relational databases. SQL is pronounced either as the word Sequel or as the letters SQL.
SQL uses simple syntax that is easy to learn and use there are five types of SQL statements given below.

Query Statements: Allow you to retrieve the rows stored in the database tables. You write a query using the SQL SELECT statement.

Data Manipulation Language (DML) Statements: Allows you to modify the contents of the tables. There are three DML statements.

• INSERT: – Allows you to insert row(s) into the Table.
• UPDATE: – Allows you to change a Row.
• DELETE: – Allows you delete the rows from the Table.

Data Definition Language (DDL): Allows you to define the Data structures, such as tables that make up a database. There are five basic types of DDL statements.

• CREATE:-Allows you to Create Database structure.
Ex: Create Table – Used to create a Table in the Database.
Create User – Used to create the database user.
• ALTER: – Allows you to modify a database structure.
• DROP: – Allows you to remove a database structure.
• RENAME: – Allows you to change the name of the table.
• TRUNCATE: – Allows you to delete the entire contents of the table.

Transaction Control (TC) Statements: Allows you to permanently record the changes made to rows stored in a table or undo the changes. There are three TC Statements.

• COMMIT: – Allows you to permanently record the changes made to the rows.
• ROLLBACK: – Allows you to undo the changes made to the rows.
• SAVEPOINT: – Allows you to set a SAVEPOINT to which you can rollback changes you made.

Data Control Language (DCL): Allows you to change the permissions on the database structures. There are two DCL statements.

• GRANT: – Allows you to give another user access to your database structures, such as tables.
• REVOKE: – Allows you to prevent.