SQL中TRUNCATE和DELETE的区别是什么?
如果你的答案是针对特定平台的,请注明。
SQL中TRUNCATE和DELETE的区别是什么?
如果你的答案是针对特定平台的,请注明。
当前回答
如果不小心使用Delete/Truncate从表中删除了所有数据。您可以回滚已提交的事务。恢复上次备份并运行事务日志,直到将要执行删除/截断操作。
以下相关信息来自一篇博客文章:
While working on database, we are using Delete and Truncate without knowing the differences between them. In this article we will discuss the difference between Delete and Truncate in Sql. Delete: Delete is a DML command. Delete statement is executed using a row lock,each row in the table is locked for deletion. We can specify filters in where clause. It deletes specified data if where condition exists. Delete activities a trigger because the operation are logged individually. Slower than Truncate because it Keeps logs Truncate Truncate is a DDL command. Truncate table always lock the table and page but not each row.As it removes all the data. Cannot use Where condition. It Removes all the data. Truncate table cannot activate a trigger because the operation does not log individual row deletions. Faster in performance wise, because it doesn't keep any logs. Note: Delete and Truncate both can be rolled back when used with Transaction. If Transaction is done, means committed then we can not rollback Truncate command, but we can still rollback Delete command from Log files, as delete write records them in Log file in case it is needed to rollback in future from log files. If you have a Foreign key constraint referring to the table you are trying to truncate, this won't work even if the referring table has no data in it. This is because the foreign key checking is done with DDL rather than DML. This can be got around by temporarily disabling the foreign key constraint(s) to the table. Delete table is a logged operation. So the deletion of each row gets logged in the transaction log, which makes it slow. Truncate table also deletes all the rows in a table, but it won't log the deletion of each row instead it logs the deallocation of the data pages of the table, which makes it faster. ~ If accidentally you removed all the data from table using Delete/Truncate. You can rollback committed transaction. Restore the last backup and run transaction log till the time when Delete/Truncate is about to happen.
其他回答
删除
DELETE是一个DML命令 DELETE可以回退 Delete =仅删除-因此可以回滚 在DELETE中,可以使用WHERE子句编写条件 语法- Delete from [Table] where [Condition]
截断
TRUNCATE是一个DDL命令 不能在TRUNCATE中回滚,TRUNCATE将永久删除该记录 Truncate = Delete+Commit -这样我们就不能回滚 不能在TRUNCATE中使用条件(WHERE子句) 语法- Truncate table [table]
详情请浏览
http://www.zilckh.com/what-is-the-difference-between-truncate-and-delete/
如果将TRUNCATE包装在事务中,则可以回滚。
请参阅下面的两个参考资料并自行测试:-
http://blog.sqlauthority.com/2007/12/26/sql-server-truncate-cant-be-rolled-back-using-log-files-after-transaction-session-is-closed/
http://sqlblog.com/blogs/kalen_delaney/archive/2010/10/12/tsql-tuesday-11-rolling-back-truncate-table.aspx
截断与删除是SQL面试中最臭名昭著的问题之一。一定要向面试官解释清楚,否则可能会让你丢掉这份工作。问题是没有多少人意识到这一点,所以如果你告诉他们YES Truncate可以回滚,他们很可能会认为答案是错误的。
在这个例子中,Truncate也可以被rollback
begin Tran
delete from Employee
select * from Employee
Rollback
select * from Employee
DELETE语句:该命令只根据where子句中给定的条件从表中删除行,如果没有指定条件,则从表中删除所有行。但是它不会释放包含表的空间。
SQL DELETE语句的语法是:
DELETE FROM table_name [WHERE condition];
TRUNCATE语句:该命令用于删除表中的所有行,并释放包含表的空间。
truncate和delete的区别如下:
+----------------------------------------+----------------------------------------------+
| Truncate | Delete |
+----------------------------------------+----------------------------------------------+
| We can't Rollback after performing | We can Rollback after delete. |
| Truncate. | |
| | |
| Example: | Example: |
| BEGIN TRAN | BEGIN TRAN |
| TRUNCATE TABLE tranTest | DELETE FROM tranTest |
| SELECT * FROM tranTest | SELECT * FROM tranTest |
| ROLLBACK | ROLLBACK |
| SELECT * FROM tranTest | SELECT * FROM tranTest |
+----------------------------------------+----------------------------------------------+
| Truncate reset identity of table. | Delete does not reset identity of table. |
+----------------------------------------+----------------------------------------------+
| It locks the entire table. | It locks the table row. |
+----------------------------------------+----------------------------------------------+
| Its DDL(Data Definition Language) | Its DML(Data Manipulation Language) |
| command. | command. |
+----------------------------------------+----------------------------------------------+
| We can't use WHERE clause with it. | We can use WHERE to filter data to delete. |
+----------------------------------------+----------------------------------------------+
| Trigger is not fired while truncate. | Trigger is fired. |
+----------------------------------------+----------------------------------------------+
| Syntax : | Syntax : |
| 1) TRUNCATE TABLE table_name | 1) DELETE FROM table_name |
| | 2) DELETE FROM table_name WHERE |
| | example_column_id IN (1,2,3) |
+----------------------------------------+----------------------------------------------+