Question

我有一个存储过程，它会联合一些数据并返回。在最大值时，SP将返回符合where条件的3行。

如果没有符合条件的数据，我是否可以强制SP返回空白行？

这就是我的SP的样子：

SELECT Top 1 Col1, 'FirstResult' FROM Table T1
       where SomeColumn='whatever'

UNION ALL

SELECT Top 1 Col2, 'SecondResult' FROM Table T1
       where SomeColumn='whatever'

UNION ALL

SELECT Top 1 Col3, 'ThirdResult' FROM Table T1
       where SomeColumn='whatever'

即使条件不匹配，我也要总是给我3行。当然，结果集中的数据将为空或NULL。

Answer 1

您可以在此处演示此答案中的查询不使用任何行：http://www.sqlfiddle.com/#!3/51d1c/3

在YourTable中有一行：http://www.sqlfiddle.com/#!3/ad1e8/1

这是一个应该返回您要找的内容的程序：

CREATE PROCEDURE pExample_Get3ForcedRows
    @FirstMatch VARCHAR(50)
    ,@SecondMatch VARCHAR(50)
    ,@ThirdMatch VARCHAR(50)
AS
BEGIN

DECLARE @ForceTable TABLE
(
    MatchColumn VARCHAR(50) NOT NULL
)

INSERT @ForceTable (MatchColumn) VALUES (@FirstMatch),(@SecondMatch),(@ThirdMatch)

SELECT
    T.Col1
    , T.ResultColumn
FROM @ForceTable F
LEFT JOIN YourTable T
    ON T.SomeColumn = F.MatchColumn

END
GO

Answer 2

DECLARE @table (Col1 varchar, String2 varchar)

IF ( (SELECT COUNT(*) FROM Table T1 WHERE SomeColumn='whatever')>0 )
  INSERT INTO @table
  SELECT Top 1 Col1, 'FirstResult' FROM Table T1 WHERE SomeColumn='whatever'
ELSE
  INSERT INTO @table
  SELECT NULL AS Col1, ''

IF ( (SELECT COUNT(*) FROM Table T1 WHERE SomeColumn='whatever')>0 )
  INSERT INTO @table
  SELECT Top 1 Col2, 'secondResult' FROM Table T1 WHERE SomeColumn='whatever'
ELSE
  INSERT INTO @table
  SELECT NULL AS Col2, ''

IF ( (SELECT COUNT(*) FROM Table T1 WHERE SomeColumn='whatever')>0 )
  INSERT INTO @table
  SELECT Top 1 Col3, 'thirdResult' FROM Table T1 WHERE SomeColumn='whatever'
ELSE
  INSERT INTO @table
  SELECT NULL AS Col3, ''

RETURN @table

不知道是否有更优雅的版本，但这应该有用。

即使条件不匹配，也始终在UNION中返回一些行

2 个答案: