带有 union all 的存储过程循环

如何解决带有 union all 的存储过程循环

我需要帮助来优化此处显示的存储过程。它可以工作，但是当它运行时，它会为每个数据库生成一个选择脚本。我需要存储过程来联合所有选择语句。

有人知道怎么做吗？

SET NOCOUNT ON;
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;

IF OBJECT_ID('tempdb.dbo.#database') IS NOT NULL
    DROP TABLE #database

CREATE TABLE #database
(
    id INT IDENTITY PRIMARY KEY,name sysname
)

SET NOCOUNT ON

BEGIN

INSERT INTO #database(name) 
    SELECT name
    FROM master.sys.databases 
    WHERE name IN (SELECT [DATABASE] COLLATE latin1_General_CI_AS  
                   FROM SETTINGS.DBO.SETTINGS
                   WHERE [KEY] = 'DB_NAME' AND SETTING = '1' )
    ORDER BY name
END

DECLARE @id INT,@cnt INT,@sql NVARCHAR(max),@currentDb sysname;

SELECT @id = 1,@cnt = MAX(id)
FROM #database

WHILE @id <= @cnt
BEGIN
    SELECT @currentDb = name
    FROM #database
    WHERE id = @id

    SET @sql =  'select * FROM ' + @currentDb + '.dbo.People'
    PRINT @sql

    EXEC (@sql);  
    
    PRINT '--------------------------------------------------------------------------'
    SET @id = @id + 1; 
END

DROP TABLE #database
END

解决方法

在循环中构建动态字符串，并且只有在循环完成后才执行它。

WHILE @id <= @cnt BEGIN
    SELECT @currentDb = [name]
    FROM #database
    WHERE id = @id;

    SET @sql = @sql + CASE WHEN LEN(@sql) > 0 THEN ' union all ' ELSE '' END
        + 'SELECT * FROM ' + QUOTENAME(@currentDb) + '.dbo.People';

    SET @id = @id + 1; 
END;
IF len(@sql) > 0 BEGIN
    print @sql
    exec (@sql); 
END;

注意使用 QUOTENAME 来防止 SQL 注入问题 - 即使只是偶然。

,

我更改了代码并复制并尝试了下面的链接，效果很好。感谢您的帮助。

How do you use a cursor to combine data in a Union All?

DECLARE @sql NVARCHAR(MAX) = N'';

SELECT @sql = @sql +
'UNION ALL SELECT column1 FROM ' + QUOTENAME(name) + '..tableA' + CHAR(10)
FROM sys.databases 
WHERE [name] NOT IN ('master','tempdb','model','msdb')

SELECT @sql = STUFF(@sql,1,10,'')

PRINT @sql
EXEC (@sql)