TSQL BINARY_CHECKSUM 作为默认值 [英] TSQL BINARY_CHECKSUM as a default value

问题描述

表中有一个列，它应该存储列列表的校验和，但我想将其创建为该表的默认值:

There is a column in a table, which should store Checksum for list of columns, but I'd like to create it as a default value for this table:

CREATE TABLE tblVitalyTest (id BIGINT IDENTITY(1,1), startTime DATETIME, value1 INT, value2 INT, value3 INT, value4 DATETIME, BinCheckSum BIGINT)
GO
ALTER TABLE tblVitalyTest ADD  DEFAULT (BINARY_CHECKSUM(value1, value2, value3, value4)) FOR [BinCheckSum]
GO

所以，应该这样使用:

INSERT INTO tblVitalyTest (startTime,value1,value2,value3,value4) VALUES ('2015-05-25',1,1,1,'2015-11-11')

结果应该是这样的:

id、startTime、value1、value2、value3、value4、BinCheckSum

id, startTime, value1, value2, value3, value4, BinCheckSum

1, "2015-05-25", 1, 1, 1, "2015-11-11", 46173

1, "2015-05-25", 1, 1, 1, "2015-11-11", 46173

但不幸的是，表默认"表创建失败.

But table "default" table creation fails unfortunately.

有一个查询可以玩:

DECLARE @a TABLE (id BIGINT IDENTITY(1,1), startTime DATETIME, value1 INT, value2 INT, value3 INT, value4 DATETIME)

INSERT INTO @a (startTime,value1,value2,value3,value4) 
    VALUES ('2015-05-25 08:00',1,1,1,'2015-11-11'),('2015-05-25 09:00',1,2,1,'2015-11-11')
          ,('2015-05-25 10:00',null,null,null,'2015-11-11'),('2015-05-25 11:00',2,1,1,'2015-11-11'),('2015-05-25 11:00',null,null,null,'2015-11-12')

SELECT a.*,BINARY_CHECKSUM(a.value1,a.value2,a.value3,a.value4) [BinCheckSum]
FROM @a a

请告诉我有没有办法创建一个 Binary_Checksum 作为列的默认值?

Please let me know is there any way to create a Binary_Checksum as a default value for the column?

推荐答案

基本上你不能.但是你可以用触发器做类似的事情.见下文

Basically you can't. But you can do something similar with a trigger. See below

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE TRIGGER dbo.tblVitalyTestUpdateInsertTrigger ON dbo.tblVitalyTest
  AFTER INSERT, UPDATE
AS
  BEGIN

    SET NOCOUNT ON;
    UPDATE
      vt
    SET
      vt.BinCheckSum = BINARY_CHECKSUM(vt.value1, vt.value2, vt.value3,
                                       vt.value4)
    FROM
      dbo.tblVitalyTest vt
      INNER JOIN INSERTED i
        ON vt.id = i.id

  END
GO

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