本文介绍了关系数据库中的五种主要语言：数据查询语言(DQL)、数据操纵语言(DML)、数据定义语言(DDL)、事务控制语言(TCL)及数据控制语言(DCL)，并列举了每种语言的具体操作命令。
关系数据库的语言
DQL: Data Query Language,
Some examples:
SELECT - retrieve data from the a database
DML: Data Manipulation Language,
Some examples:
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes all records from a table, the space for the records remain
DDL: Data Definition Language,
Some examples:
CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
TCL: Transaction Control Language,
Some examples:
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
DCL: Data Control Language.
Some examples:
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command
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