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SQL Tutorial

SQL is a standard language for accessing and manipulating databases. It includes database creation, deletion, fetching rows and modifying rows etc. SQL is stands for Structured Query Language.

SQL is an ANSI (American National Standards Institute) standard but there are many different versions of the SQL language.

SQL is the standard database language for Relation Database System like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server etc. The data in RDBMS is stored in tables. A table is a collection of related data entries in the form of columns and rows.

The SQL language has several parts:

  • Data Definition Language (DDL)

    The SQL DDL provides commands for defining relation schemas, deleting relations, and modifying relation schema.

    CREATE Creates a new table, a view of a table, or other object in database
    ALTER Modifies an existing database object, such as a table.
    DROP Deletes an entire table, a view of a table or other object in the database.

  • Data Manipulation Language (DML)

    The SQL DML includes a query language based on both the relational algebra and the tuple relational calculus. It includes also commands to insert tuples into, delete tuples from, and modify tuples in the database.

    Command Description
    SELECT Retrieves certain records from one or more tables
    INSERT Creates a record
    UPDATE Modifies records
    DELETE Deletes records

  • Data Control Language (DCL)

    It provides commands to control access to data stored in a database.

    GRANT Gives a privilege to user
    REVOKE Takes back privileges granted from user

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