对于SQL Server或MySQL，如果有一个带有自动递增的PK, truncate将重置计数器。

并不是说截断不记录SQL Server中的任何内容。truncate不记录任何信息，但它记录您触发truncate的表的数据页的释放。

如果在开始时定义事务，则可以回滚被截断的记录，回滚后可以恢复被截断的记录。但不能在提交截断事务后从事务日志备份中恢复截断记录。

DROP The DROP command removes a table from the database. All the tables' rows, indexes and privileges will also be removed. No DML triggers will be fired. The operation cannot be rolled back. TRUNCATE TRUNCATE removes all rows from a table. The operation cannot be rolled back and no triggers will be fired. As such, TRUNCATE is faster and doesn't use as much undo space as a DELETE. Table level lock will be added when Truncating. DELETE The DELETE command is used to remove rows from a table. A WHERE clause can be used to only remove some rows. If no WHERE condition is specified, all rows will be removed. After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it. Note that this operation will cause all DELETE triggers on the table to fire. Row level lock will be added when deleting.

来自:http://www.orafaq.com/faq/difference_between_truncate_delete_and_drop_commands

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)              |
+----------------------------------------+----------------------------------------------+

对原始答案的一个小修正——删除也会产生大量的重做(因为undo本身是由重做保护的)。这可以从autotrace输出中看到:

SQL> delete from t1;

10918 rows deleted.

Elapsed: 00:00:00.58

Execution Plan
----------------------------------------------------------
   0      DELETE STATEMENT Optimizer=FIRST_ROWS (Cost=43 Card=1)
   1    0   DELETE OF 'T1'
   2    1     TABLE ACCESS (FULL) OF 'T1' (TABLE) (Cost=43 Card=1)




Statistics
----------------------------------------------------------
         30  recursive calls
      12118  db block gets
        213  consistent gets
        142  physical reads
    3975328  redo size
        441  bytes sent via SQL*Net to client
        537  bytes received via SQL*Net from client
          4  SQL*Net roundtrips to/from client
          2  sorts (memory)
          0  sorts (disk)
      10918  rows processed

Truncate命令用于重新初始化表，它是一个删除表中所有行的DDL命令。DELETE是一个DML命令，用于根据某些条件删除一行或一组行，如果没有指定condition，则该命令将删除表中的所有行。