先决条件– DDL,DML,TCL和DCL
1.数据操作语言(DML):
DML用于处理数据库中的数据。例如,在SQL中插入,更新和删除指令。
2.交易控制语言(TCL):
TCL处理数据库内的事务。
DML和TCL之间的区别:
S. no. | Category | DML | TCL | ||||
---|---|---|---|---|---|---|---|
1. | Full Form | DML stands for Data Manipulation Language. | TCL stands for Transaction Control Language. | ||||
2. | Definition | DML stands for Data Manipulation Language and is used to manipulate data in the database by performing insertion, updating and deletion operations. | Transaction Control Language (TCL) consists of commands that deal with the transactions within databases. | 3. | Classification | Data Modification Language is further classified into Procedural and Non-Procedural DML. | Transaction Control Language doesn’t have any further classifications. |
4. | DBMS feature exhibited | It exhibits the feature of easy maintenance (of files). | It exhibits the feature of Atomicity. | ||||
5. | Use in Transactions | DML cannot be used for database transactions. | TCL is used for handling database transactions. | ||||
6. | Order | DML statements are usually written before TCL statements in a Query. | TCL statements are usually written after DML statements in a Query. | ||||
7. | Use of Log files | It does not use Log files. | It uses log files to keep a record of all transactions. | ||||
8. | Commands | Frequently used commands present in DML are: UPDATE, INSERT, MERGE, SELECT, DELETE, CALL, EXPLAIN PLAN, LOCK TABLE. | Frequently used commands present in TCL are: COMMIT, ROLLBACK, SAVEPOINT, SET TRNSACTION. | ||||
9. | Handled by | DML is handled by the Query Compiler and Query Optimizer part of the DBMS architecture. | TCL is handled by the Transaction Manager and Recovery Manager. | ||||
10. | Locking | It uses Locks for concurrency control. | It does not use Locks. | ||||
11. | WHERE clause | Most DML statements have WHERE clause to filter them. | TCL does not need WHERE clause. | ||||
12. | Data Access Paths | DML can be used to explain access paths to data. | TCL cannot explain data access paths. | ||||
13. | Call a subprogram | It is used to call PL/SQL or Java subprogram. | It is not used to call subprograms. | ||||
14. | Merge operation | We can perform Merge operation using DML. | TCL cannot perform Merge operations. | ||||
15. | Trigger | Triggers are fired after DML statements. | TCL is not used for triggers. | 16. | Example | Example of SQL query that finds the names of all instructors in the History department : SELECT name FROM instructor WHERE dept_name = ‘History’; |
We will use commit command to save the table record permanently. Incase we want to update the name Jolly to sherlock and save it permanently, we would use the following, UPDATE STUDENT SET NAME = ‘Sherlock’ WHERE NAME = ‘Jolly’; COMMIT; |