SQL點滴24 監測表的變更。本站提示廣大學習愛好者：（SQL點滴24 監測表的變更）文章只能為提供參考，不一定能成為您想要的結果。以下是SQL點滴24 監測表的變更正文
有時刻，我們在某一主要的時光段須要監控某張表的變更情形，包括拔出、更新、刪除。舉例來講，當我們把數據導出到內部的體系時，我們願望導出的是全體的數據，並且最好是導出前次導出以後更改的數據。
作為DBA，我們可采傳統的觸發器操作，來構建一個元數據表或一個時光戳列來監控數據的變更。
代碼以下：Code Listing 1
該代碼在 SQL 2005(SP3), SQL 2008 R2 (RTM with cu5)測試經由過程
-------------------
--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
比來我正在讀關天SQLSERVER在線贊助（BOL）相干的常識, 我接觸到了 SQL Server CHECKSUM(), BINARY_CHECKSUM(), and CHECKSUM_AGG() 這幾個函數, 由此忽然想到這些函數是否是也能夠監控表的數據變更，而現實證實CHECKSUM_AGG() 函數雖然被描寫為檢測表的變更，但這裡不實用.
應用 CheckSum() and CheckSum_Agg() 函數
CHECKSUM_AGG() 函數, 在Books OnLine 和很多相干的站點上是如許描寫的, 平日用於檢測一個表的數據能否更改. 這是一個取代觸發器的更好的辦法，只是該操作會惹起表掃描的操作。因而我此次我依然應用元數據來跟蹤數據的變更，只是新建了列LastChkSum取代了LastUpdate,該列用於保留CHECKSUM_AGG(BINARY_CHECKSUM(*)),它將會在全表中發生一個獨一值，以差別數據的變更情形。
代碼以下： Listing 2.
---------------------------------------------
--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
正如你所看到的那樣，關於單個的變更的情形，CHECKSUM是應用比擬好的，然則CHECKSUM_AGG()卻不克不及反響數據的變更
代碼以下：Code Listing 3
--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
我們會發明調劑前後 CHECKSUM_AGG(BINARY_CHECKSUM(*)) 的值是一樣的，不克不及辨別
結論：
CHECKSUM_AGG() 函數雖然被描寫為能監測表數據的變更，在現實測試中是不可的。特別是對表停止對稱數據修正時，沒法監測
作者：Tyler Ning
