SqlServer 利用游标批量更新数据

Intro

游标在有时候会很有用，在更新一部分不多的数据时，可以很方便的更新数据，不需要再写一个小工具来做了，直接写 SQL 就可以了

Sample

下面来看一个实际示例：

-- 声明字段变量
DECLARE @RegionCode INT;
DECLARE @RegionName NVARCHAR(64);
DECLARE @ProvinceId INT;

-- 声明游标
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
);

-- 打开游标
OPEN ProvinceCursor;

-- 移动游标，加载数据
FETCH NEXT FROM ProvinceCursor
INTO @ProvinceId,@RegionCode,@RegionName;

WHILE @@FETCH_STATUS = 0
BEGIN
    -- 根据游标数据进行操作，这里只输出要执行的 SQL 脚本，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) +';';
	
        -- 移动游标到下一条数据
        FETCH NEXT FROM ProvinceCursor
	INTO @ProvinceId,@RegionCode,@RegionName;
END;
CLOSE ProvinceCursor;
DEALLOCATE ProvinceCursor;

Another Sample

DECLARE @projectId nvarchar(36)  -- 声明变量
DECLARE My_Cursor CURSOR --定义游标
FOR (SELECT OriginalProjectId FROM dbo.CommunityProjects
WHERE CommunityId = -1) --查出需要的集合放到游标中
OPEN My_Cursor; --打开游标
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; --关闭游标
DEALLOCATE My_Cursor; --释放游标

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

在做一些小数据量的数据操作时，游标会非常方便，而且游标比较灵活，你可以只生成更新数据的SQL，也可以打印出数据更新前后的值，以便错误更新数据之后的数据恢复

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/