SQL点滴24 监测表的变化

有时候，我们在某一重要的时间段需要监控某张表的变化情况，包含插入、更新、删除。举例来说，当我们把数据导出到外部的系统时，我们希望导出的是全部的数据，而且最好是导出上次导出之后变动的数据。

作为DBA，我们可采传统的触发器操作，来构建一个元数据表或一个时间戳列来监控数据的变化。

代码如下：Code Listing 1

该代码在 SQL 2005(SP3), SQL 2008 R2 (RTM with cu5)测试通过

复制代码代码如下:

——————-

–Method 1: TRIGGER

——————-

–Base Table Definition

IF OBJECT_ID(‘CheckSumTest’, ‘U’) IS NOT NULL DROP TABLE CheckSumTest

GO

CREATE TABLE CheckSumTest

(

id int IDENTITY(1,1) NOT NULL PRIMARY KEY,

vc1 varchar(1) NOT NULL,

vc2 varchar(1) NOT NULL

)

GO

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘a’, ‘b’

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘b’, ‘a’

GO

–Create Audit Summary Table to hold Meta-Data

IF OBJECT_ID(‘dbo.TableAuditSummary’, ‘U’) IS NOT NULL DROP TABLE dbo.TableAuditSummary

CREATE TABLE dbo.TableAuditSummary

( id INT IDENTITY(1,1) NOT NULL PRIMARY KEY,

TableName sysname NOT NULL,

LastUpdate DATETIME NOT NULL,

LastExport DATETIME NOT NULL

)

GO

INSERT dbo.TableAuditSummary (TableName, LastUpdate, LastExport) VALUES (‘dbo.CheckSumTest’, GETDATE(), GETDATE())

GO

–Tables that need exporting

SELECT * FROM dbo.TableAuditSummary WHERE LastUpdate>LastExport

–Create Trigger on all Base Tables

–This fires on any insert/update/delete and writes new LastUpdate column for the table set to Current Date and Time

IF OBJECT_ID(‘dbo.trg_CheckSumTest_MaintainAuditSummary’, ‘TR’) IS NOT NULL DROP TRIGGER dbo.trg_CheckSumTest_MaintainAuditSummary

GO

CREATE TRIGGER dbo.trg_CheckSumTest_MaintainAuditSummary

ON dbo.CheckSumTest

AFTER INSERT, UPDATE, DELETE

AS

BEGIN

IF (object_id(‘dbo.CheckSumTest’) IS NOT NULL)

UPDATE dbo.TableAuditSummary SET LastUpdate=GETDATE() WHERE TableName=’dbo.CheckSumTest’

END

GO

–Make an Update

UPDATE dbo.CheckSumTest SET vc1=’b’, vc2=’a’ WHERE id=1

UPDATE dbo.CheckSumTest SET vc1=’a’, vc2=’b’ WHERE id=2

–Check Meta-Data

SELECT * FROM dbo.TableAuditSummary WHERE LastUpdate>LastExport

–When we have Exported the data, we run the following to reset MetaData

UPDATE dbo.TableAuditSummary SET LastExport=GETDATE() WHERE LastUpdate>LastExport

最近我正在读关天SQLSERVER在线帮助（BOL）相关的知识, 我接触到了 SQL Server CHECKSUM(), BINARY_CHECKSUM(), and CHECKSUM_AGG() 这几个函数, 由此突然想到这些函数是不是也可以监控表的数据变化，而事实证明CHECKSUM_AGG() 函数尽管被描述为检测表的变化，但这里不适用.

使用 CheckSum() and CheckSum_Agg() 函数

CHECKSUM_AGG() 函数, 在Books OnLine 和许多相关的站点上是这样描述的, 通常用于检测一个表的数据是否更改. 这是一个代替触发器的更好的方法，只是该操作会引起表扫描的操作。于是我这次我仍然使用元数据来跟踪数据的变化，只是新建了列LastChkSum代替了LastUpdate,该列用于保存CHECKSUM_AGG(BINARY_CHECKSUM(*)),它将会在全表中产生一个唯一值，以区别数据的变化情况。

代码如下： Listing 2.

复制代码代码如下:

———————————————

–Method 2 : using CheckSum (not reliable)

———————————————

–Base Table Definition

IF OBJECT_ID(‘CheckSumTest’, ‘U’) IS NOT NULL DROP TABLE CheckSumTest

GO

CREATE TABLE CheckSumTest

(

id int IDENTITY(1,1) NOT NULL PRIMARY KEY,

vc1 varchar(1) NOT NULL,

vc2 varchar(1) NOT NULL

)

GO

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘a’, ‘b’

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘b’, ‘a’

GO

–Create Audit Summary Table to hold Meta-Data

IF OBJECT_ID(‘dbo.TableAuditSummary’, ‘U’) IS NOT NULL DROP TABLE dbo.TableAuditSummary

CREATE TABLE dbo.TableAuditSummary

( id INT IDENTITY(1,1) NOT NULL PRIMARY KEY,

TableName sysname NOT NULL,

LastChkSum INT NOT NULL

)

GO

INSERT dbo.TableAuditSummary (TableName, LastChkSum)

SELECT ‘dbo.CheckSumTest’, CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM dbo.CheckSumTest

GO

–Tables that need exporting

SELECT * FROM dbo.TableAuditSummary WHERE TableName=’dbo.CheckSumTest’

AND LastChkSum<>(SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM dbo.CheckSumTest)

UNION ALL

…

–Make a Simple (Single row) Update

UPDATE dbo.CheckSumTest SET vc1=’c’, vc2=’a’ WHERE id=1

–Tables that need exporting

SELECT * FROM dbo.TableAuditSummary WHERE TableName=’dbo.CheckSumTest’

AND LastChkSum<>(SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM dbo.CheckSumTest)

UNION ALL

…

–Reset MetaData

UPDATE dbo.TableAuditSummary SET LastChkSum=(SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM dbo.CheckSumTest)

WHERE TableName=’dbo.CheckSumTest’

–Make a Symmetric change

UPDATE dbo.CheckSumTest SET vc1=’b’, vc2=’a’ WHERE id=1

UPDATE dbo.CheckSumTest SET vc1=’c’, vc2=’a’ WHERE id=2

–Tables that need exporting (no rows returned as CHECKSUM_AGG() has not changed!!)

SELECT * FROM dbo.TableAuditSummary WHERE TableName=’dbo.CheckSumTest’

AND LastChkSum<>(SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM dbo.CheckSumTest)

UNION ALLCode Listing 2

正如你所看到的那样，对于单个的变化的情况，CHECKSUM是使用比较好的，但是CHECKSUM_AGG()却不能反应数据的变化

代码如下：Code Listing 3

复制代码代码如下:

–Base Table Definition

IF OBJECT_ID(‘CheckSumTest’, ‘U’) IS NOT NULL DROP TABLE CheckSumTest

GO

CREATE TABLE CheckSumTest

(

id int IDENTITY(1,1) NOT NULL PRIMARY KEY,

vc1 varchar(1) NOT NULL,

vc2 varchar(1) NOT NULL,

chksum1 AS (CHECKSUM(id, vc1, vc2)),

chksum2 AS (BINARY_CHECKSUM(id, vc1, vc2))

)

GO

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘a’, ‘b’

INSERT dbo.CheckSumTest (vc1, vc2) SELECT ‘b’, ‘a’

GO

–Show Computed Columns and CheckSum_Agg() value = 199555

SELECT * FROM CheckSumTest

SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM CheckSumTest

–Make a Simple (Single row) Update

UPDATE dbo.CheckSumTest SET vc1=’c’, vc2=’a’ WHERE id=1

–Show Computed Columns and CheckSum_Agg() value = 204816 (Ok)

SELECT * FROM CheckSumTest

SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM CheckSumTest

–Make a Symmetric change

UPDATE dbo.CheckSumTest SET vc1=’b’, vc2=’a’ WHERE id=1

UPDATE dbo.CheckSumTest SET vc1=’c’, vc2=’a’ WHERE id=2

–Show Computed Columns and CheckSum_Agg() value = 204816 (Not Ok!)

SELECT * FROM CheckSumTest

SELECT CHECKSUM_AGG(BINARY_CHECKSUM(*)) FROM CheckSumTest