我已经将记录插入到SQL Server数据库表中。该表定义了一个主键,并且自动递增标识种子被设置为“Yes”。这样做主要是因为在SQL Azure中,每个表都必须定义一个主键和标识。

但是由于我必须从表中删除一些记录,这些表的标识种子将受到干扰,索引列(自动生成的增量为1)也将受到干扰。

如何在删除记录后重置标识列,使该列具有升序数字顺序?

标识列在数据库中的任何地方都不能用作外键。


当前回答

对于一个完整的DELETE行和重置IDENTITY计数,我使用这个(SQL Server 2008 R2)

USE mydb

-- ##################################################################################################################
-- DANGEROUS!!!! USE WITH CARE
-- ##################################################################################################################

DECLARE
  db_cursor CURSOR FOR
    SELECT TABLE_NAME
      FROM INFORMATION_SCHEMA.TABLES
     WHERE TABLE_TYPE = 'BASE TABLE'
       AND TABLE_CATALOG = 'mydb'

DECLARE @tblname VARCHAR(50)
SET @tblname = ''

OPEN db_cursor
FETCH NEXT FROM db_cursor INTO @tblname

WHILE @@FETCH_STATUS = 0
BEGIN
  IF CHARINDEX('mycommonwordforalltablesIwanttodothisto', @tblname) > 0
    BEGIN
      EXEC('DELETE FROM ' + @tblname)
      DBCC CHECKIDENT (@tblname, RESEED, 0)
    END

  FETCH NEXT FROM db_cursor INTO @tblname
END

CLOSE db_cursor
DEALLOCATE db_cursor
GO

其他回答

截断表是首选,因为它可以清除记录,重置计数器并回收磁盘空间。

Delete和CheckIdent应该只在外键阻止截断的情况下使用。

DBCC CHECKIDENT ('TestTable', RESEED, 0)
GO

其中0是标识起始值

在可能的情况下使用TRUNCATE总是比删除所有记录更好,因为它也不使用日志空间。

如果我们需要删除和重置种子,请记住,如果表从未被填充,并且您使用DBCC CHECKIDENT('tablenem',RESEED,0) 那么第一条记录将得到identity = 0 如MSDN文档所述

在您的情况下,只重建索引,而不用担心丢失 级数恒等式这样的情况很常见。

DBCC CHECKIDENT management命令用于重置标识计数器。命令格式为:

DBCC CHECKIDENT (table_name [, { NORESEED | { RESEED [, new_reseed_value ]}}])
[ WITH NO_INFOMSGS ]

例子:

DBCC CHECKIDENT ('[TestTable]', RESEED, 0);
GO

以前版本的Azure SQL数据库不支持,但现在支持了。


多亏了Solomon Rutzky,该命令的文档现在已经修复。

需要注意的是,如果所有的数据都是通过DELETE从表中删除的(即没有WHERE子句),那么只要a)权限允许,b)没有fk引用表(这里似乎就是这种情况),使用TRUNCATE table将是首选,因为它可以更有效地DELETE并同时重置IDENTITY种子。以下细节取自TRUNCATE TABLE的MSDN页面:

Compared to the DELETE statement, TRUNCATE TABLE has the following advantages: Less transaction log space is used. The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log. Fewer locks are typically used. When the DELETE statement is executed using a row lock, each row in the table is locked for deletion. TRUNCATE TABLE always locks the table (including a schema (SCH-M) lock) and page but not each row. Without exception, zero pages are left in the table. After a DELETE statement is executed, the table can still contain empty pages. For example, empty pages in a heap cannot be deallocated without at least an exclusive (LCK_M_X) table lock. If the delete operation does not use a table lock, the table (heap) will contain many empty pages. For indexes, the delete operation can leave empty pages behind, although these pages will be deallocated quickly by a background cleanup process. If the table contains an identity column, the counter for that column is reset to the seed value defined for the column. If no seed was defined, the default value 1 is used. To retain the identity counter, use DELETE instead.

下面是:

DELETE FROM [MyTable];
DBCC CHECKIDENT ('[MyTable]', RESEED, 0);

变成:

TRUNCATE TABLE [MyTable];

请参阅TRUNCATE TABLE文档(上面有链接)以获得有关限制等的其他信息。