先决条件– SQL命令
1.数据定义语言(DDL):
顾名思义,数据定义语言用于定义数据库模式。例如:create table,alter table是SQL中的一些DDL指令。
2.交易控制语言(TCL):
顾名思义,事务控制语言包含用于管理数据库中事务的命令。 DDL和TCL之间的区别:
S.No. | DDL | TCL |
---|---|---|
1. | It stands for Data Definition Language. | It stands for Transaction Control Language. |
2. | It is used to define data structures or overall database schema. | It contains those commands, which are used to manage transactions within the database. |
3. | By using DDL commands, database transactions cannot be handled. | TCL commands are meant to handle database transactions. |
4. | Files can be easily maintained by DDL commands. | It manages the different tasks with the important feature, Atomicity. |
5. | While writing any query, usually DDL statements are written before TCL statements. | Usually, TCL statements are written before DDL statements. |
6. | DDL does not require any log files to maintain the database. | It uses log files to keep track of records of all transactions in a database. |
7. | Some DDL commands which are frequently used : CREATE, ALTER, DROP. | Some TCL commands which are frequently used : COMMIT, ROLLBACK. |