Question

当我运行此查询时，我收到此错误：

程序sp_GET_RANDOM_QUESTIONS，第40行当未使用EXISTS引入子查询时，只能在选择列表中指定一个表达式。消息116，级别16，状态1，过程sp_GET_RANDOM_QUESTIONS，第52行当未使用EXISTS引入子查询时，只能在选择列表中指定一个表达式。

这是一个存储过程，用于提供随机问题，@ easy，@ medium，@ hard是随机化的问题数。如果用户选择只给出@num，我会将该数字除以3（3个难产）并得到那些随机问题。

SELECT  case
WHEN @num=0 THEN (
    SELECT * FROM (
    SELECT top (@easy) * from TBL_PERGUNTAS as p where p.category=1 order by NEWID()) as a
    UNION ALL SELECT * FROM
    (SELECT top (@medium) * from TBL_PERGUNTAS as p where p.category=2 order by NEWID()) as b
    UNION ALL SELECT * FROM
    (SELECT top (@hard) * from TBL_PERGUNTAS as p where p.category=3 order by NEWID()) as c)
    else (
    SELECT * FROM
    (SELECT top (@num/3) * from TBL_PERGUNTAS as p where p.category=1 order by NEWID()) as a
    UNION ALL SELECT * FROM
    (SELECT top (@num/3) * from TBL_PERGUNTAS as p where p.category=2 order by NEWID()) as b
    UNION ALL SELECT * FROM
    (SELECT top (@num/3) * from TBL_PERGUNTAS as p where p.category=3 order by NEWID()) as c )
END

Answer 1

正如评论所述，你需要使用IF/ELSE来控制流量，试试这个：

IF @num=0 THEN 
BEGIN
    SELECT top (@easy) * 
    FROM TBL_PERGUNTAS as p 
    WHERE p.category=1 
    ORDER BY NEWID()

    UNION ALL 

    SELECT top (@medium) * 
    FROM TBL_PERGUNTAS as p 
    WHERE p.category=2 
    ORDER BY NEWID()

    UNION ALL 

    SELECT top (@hard) * 
    FROM TBL_PERGUNTAS as p 
    WHERE p.category=3 
    ORDER BY NEWID())
END
ELSE
BEGIN
    SELECT top (@num/3) * 
    FROM TBL_PERGUNTAS as p 
    WHERE p.category=1 
    ORDER BY NEWID()

    UNION ALL 

    SELECT top (@num/3) * 
    FROM TBL_PERGUNTAS as p
    WHERE p.category=2 
    ORDER BY NEWID()

    UNION ALL  

    SELECT top (@num/3) * 
    FROM TBL_PERGUNTAS as p 
    WHERE p.category=3 
    ORDER BY NEWID())
END

在切除SELECT CASE时出错

1 个答案: