what is the diffrence between truncate and delete in sql server?

Can anybody provide me the list of all the differences b开发者_如何学Pythonetween truncate and delete in SQL server?

You should google it before asking.

Truncate

1. Truncate removes all the references from database.
2. Fast
3. No entry in transaction log.
4. Cannot be recovered if removed once.
5. Page refrences are cleared.
6. All or none
7. Identity column gets re-initialized to seed
8. Truncate is DDL

Truncate Table tblName

No contidion can be given

Delete

1. Entries are made at Transaction log.
2. Recoverable
3. Slow
4. Per record based deletion
5. References are mainained in page
6. Identity starts from its previous position
7. DML

Delete FROM tableName

None of the two effects any structure to table. All references must be removed before performing any of the operation, although it doesn't applies to delete when used with Cascade = true for delete

While working on database, we are using Delete and Truncate without knowing the differences between them and when to use 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 from log files, 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.

Check this Article Rollback Table after Truncate Command in Sql or

difference-between-delete-truncate-in

Also see when-to-use-truncate-and-delete-command

The difference between truncate and delete is listed below:

+----------------------------------------+----------------------------------------------+
|                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.      | Truncate 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)              |
+----------------------------------------+----------------------------------------------+