簡介
在SQL Server 資料庫之間複製資料時,有必要識別已修改的欄位。預設機制 COLUMNS_UPDATED 提供更新欄位的位元表示。但是,本文提供了另一種方法來檢索僅包含更新的列值的 XML 程式碼段。
自訂更新觸發器函數
要實現此目的,請建立自訂更新觸發函數如下:
CREATE TRIGGER DBCustomers_Insert ON DBCustomers AFTER UPDATE AS BEGIN DECLARE @sql as NVARCHAR(1024); SET @sql = 'SELECT '; WITH UpdatedColumns AS ( SELECT c.name AS ColumnName FROM sys.columns AS c JOIN inserted AS i ON c.object_id = i.object_id WHERE c.is_identity = 0 AND i.Original_value <> i.value ) SELECT @sql = @sql + ',' + ColumnName FROM UpdatedColumns SET @sql = $sql + ' FROM inserted FOR XML RAW'; DECLARE @x as XML; SET @x = CAST(EXEC(@sql) AS XML); .. use @x END
替代解決方案,無需COLUMNS_UPDATED
代替COLUMNS_UPDATED,另一種方法包括取消透視插入和刪除的表、連接它們以及過濾任何更改:
CREATE TRIGGER TriggerName ON dbo.Sample_Table FOR DELETE, INSERT, UPDATE AS BEGIN SET NOCOUNT ON; WITH deleted_unpvt AS ( SELECT ContactID, FieldName, FieldValue FROM (SELECT ContactID , cast(Forename as sql_variant) Forename , cast(Surname as sql_variant) Surname , cast(Extn as sql_variant) Extn , cast(Email as sql_variant) Email , cast(Age as sql_variant) Age FROM deleted) p UNPIVOT (FieldValue FOR FieldName IN (Forename, Surname, Extn, Email, Age) ) AS deleted_unpvt ), inserted_unpvt AS ( SELECT ContactID, FieldName, FieldValue FROM (SELECT ContactID , cast(Forename as sql_variant) Forename , cast(Surname as sql_variant) Surname , cast(Extn as sql_variant) Extn , cast(Email as sql_variant) Email , cast(Age as sql_variant) Age FROM inserted) p UNPIVOT (FieldValue FOR FieldName IN (Forename, Surname, Extn, Email, Age) ) AS inserted_unpvt ) INSERT INTO Sample_Table_Changes (ContactID, FieldName, FieldValueWas, FieldValueIs) SELECT Coalesce (D.ContactID, I.ContactID) ContactID , Coalesce (D.FieldName, I.FieldName) FieldName , D.FieldValue as FieldValueWas , I.FieldValue AS FieldValueIs FROM deleted_unpvt d FULL OUTER JOIN inserted_unpvt i on D.ContactID = I.ContactID AND D.FieldName = I.FieldName WHERE D.FieldValue <> I.FieldValue --Changes OR (D.FieldValue IS NOT NULL AND I.FieldValue IS NULL) -- Deletions OR (D.FieldValue IS NULL AND I.FieldValue IS NOT NULL) -- Insertions END
以上是如何在SQL Server複製中有效率地只檢索更新的欄位?的詳細內容。更多資訊請關注PHP中文網其他相關文章!