Components of SQL

Following is the four components of SQL

1. DDL
• DDL - Data Definition Language
• This is a set of command, which is used to create, modify and delete database structures data is not included.
• Examples:
• CREATE : used to create object in the database
• ALTER : alter/modify the structure of the database
• DROP : delete object from the database
• TRUNCATE : delete all records from a table and remove all spaces allocated for the records.
• COMMENT : Add comments
• GRANT : Give users access privileges to database
• REVOKE : Remove access privileges given with the GRANT command.
2. DML
• DML - Data Manipulation Language
• It is used to change data within the database
• Examples:
• INSERT : insert data into a table
• UPDATE : update existing data within a table
• DELETE : deletes all records from a table, space for the records remain as itis.
• CALL : call a PL/SQL or java program
• EXPLAIN PLAN : explain access path to data
• LOCK : table control concurrency.
3. DCL
• DCL - Data Control Language
• DCL is component of SQL statement which is control access to data and to the database
• DCL statements are grouped with DML statements.
• Example:
• COMMIT : save work done
• SAVEPOINT : identify a point in a transaction to which you can later roll back.
• ROLLBACK : restore database to original since the last COMMIT
• SET TRANSACTION : change transaction option like what rollback segment to use
• GRANT / REVOKE : grant or take back permissions to or from the oracle users.
4. DQL
• DQL - Data Query Language
• DQL used to getting data from database.
• Example:
• SELECT : retrieve data from the database.