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  • Introduction to SQL

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    Overview of SQL : SQL is a scripting language for the database handling. SQL is called as Structured Query Language. SQL is used to handle relational database, we can create, update, delete, and fetch records from the database. SQL is a powerful and very widely used database language.

    You can think SQL as a standard language to communicate with the relational database systems. There are different relational database management systems available in the market like MS Access, MS SQL Server, PostgresSql, Oracle and Sybase etc. uses the Sql as standard language.

    Type of SQL Statements :

    • DDL (Data Definition Language)
    • DML (Data Manipulation Language)
    • DCL (Data Control Language)
    • TCL (Transaction Control Language).

    1) DDL : DDL statements are used to deal with schema and structure of database. Following are the mostly used statements :

    • CREATE : statement is used to create a new database schema.

    • ALTER : statement is used to alter the database schema.

    • DROP : statement is used to drop or delete the database schema.

    • TRUNCATE : statement is used to truncate(empty) the database schema or table.

    • RENAME : statement is used to rename the database schema or table.

    2) DML : DML statements are used to manipulate the data of the database object. Following are mostly used statements :

    • SELECT : statement fetches the data from the database.

    • INSERT : statement insert the data to the database.

    • UPDATE : statement update the data in the database.

    • DELETE : statement deletes the data from the databaes.

    • CALL : statement call the PL/SQL statements.

    • LOCK TABLE : to handle the data cuncurrency.

    • MERGE :

    3) DCL : The following commands are come under Data Control Language

    • GRANT : statement used to grant access privillages to the db users.

    • REVOKE : statement used to remove the given db access privillages to the user.

    4) TCL : TCL statements forces the database to fulfil the ACID property. Following commands comes under the TCL.

    • COMMIT : to commit or save data into database.

    • ROLLBACK : using this statement we can rollback the database to the point where last commited.

    • SAVEPOINT : can set a point from where we can rollback later if needed.


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