SqlServer 利用游標批量更新數據

Intro

游標在有時候會很有用，在更新一部分不多的數據時，可以很方便的更新數據，不需要再寫一個小工具來做了，直接寫 SQL 就可以了

Sample

下麵來看一個實際示例：

-- 聲明欄位變數
DECLARE @RegionCode INT;
DECLARE @RegionName NVARCHAR(64);
DECLARE @ProvinceId INT;

-- 聲明游標
DECLARE ProvinceCursor CURSOR FOR(
SELECT Id AS ProvinceId, region.RegionCode,region.RegionName FROM dbo.Provinces AS province
JOIN dbo.Regions AS region ON province.Name=SUBSTRING(region.RegionName,1, LEN(province.Name)) AND region.RegionType=1
);

-- 打開游標
OPEN ProvinceCursor;

-- 移動游標，載入數據
FETCH NEXT FROM ProvinceCursor
INTO @ProvinceId,@RegionCode,@RegionName;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- 根據游標數據進行操作，這裡只輸出要執行的 SQL 腳本，也可以直接 UPDATE，看自己需要

    PRINT 'UPDATE dbo.Provinces SET Code = ' + CONVERT(NVARCHAR(12), @RegionCode)+', Name = N'''+@RegionName +''' WHERE Id = ' + CONVERT(NVARCHAR(12), @provinceId) +';';
    
        -- 移動游標到下一條數據
        FETCH NEXT FROM ProvinceCursor
    INTO @ProvinceId,@RegionCode,@RegionName;
END;
CLOSE ProvinceCursor;
DEALLOCATE ProvinceCursor;

Another Sample

DECLARE @projectId nvarchar(36)  -- 聲明變數
DECLARE My_Cursor CURSOR --定義游標
FOR (SELECT OriginalProjectId FROM dbo.CommunityProjects
WHERE CommunityId = -1) --查出需要的集合放到游標中
OPEN My_Cursor; --打開游標
FETCH NEXT FROM My_Cursor INTO @projectId;
WHILE @@FETCH_STATUS = 0
    BEGIN
        UPDATE dbo.CommunityProjects
        SET CommunityId = CAST(ISNULL((
            SELECT ZhongyiCommunityId FROM dbo.CommunityMappings
            WHERE FangdiCommunityId = @projectId
        ),'-1') AS INT)
        WHERE OriginalProjectId = @projectId

        FETCH NEXT FROM My_Cursor INTO @projectId;
    END
CLOSE My_Cursor; --關閉游標
DEALLOCATE My_Cursor; --釋放游標

and more

DECLARE @RegionCode INT;
DECLARE @RegionName NVARCHAR(64);
DECLARE @provinceId INT;
DECLARE ProvinceCursor CURSOR FOR(
SELECT RegionCode,
       RegionName
FROM dbo.Regions
WHERE RegionType = 1);
OPEN ProvinceCursor;
FETCH NEXT FROM ProvinceCursor
INTO @RegionCode,
     @RegionName;

WHILE @@FETCH_STATUS = 0
BEGIN
    SET @provinceId =ISNULL((SELECT Id FROM dbo.Provinces WHERE Name = @RegionName), 0);
    IF @provinceId > 0
        PRINT 'UPDATE dbo.Provinces SET Code = ' + CONVERT(NVARCHAR(12), @RegionCode)+' WHERE Id = ' + CONVERT(NVARCHAR(12), @provinceId) +';';
    ELSE
        PRINT 'INSERT INTO dbo.Provinces(Name,Code) VALUES(N''' + @RegionName + ''',' + CONVERT(NVARCHAR(12), @RegionCode)+ ');';
    FETCH NEXT FROM ProvinceCursor
    INTO @RegionCode,
         @RegionName;
END;
CLOSE ProvinceCursor;
DEALLOCATE ProvinceCursor;

More

在做一些小數據量的數據操作時，游標會非常方便，而且游標比較靈活，你可以只生成更新數據的SQL，也可以列印出數據更新前後的值，以便錯誤更新數據之後的數據恢復

Reference

• https://www.cnblogs.com/xielong/p/5941595.html
• https://www.cnblogs.com/mrma/p/3794520.html
• https://www.sqlservertutorial.net/sql-server-stored-procedures/sql-server-cursor/
• https://www.mssqltips.com/sqlservertip/1599/sql-server-cursor-example/