Question

我需要从一个乐队列表中显示键盘播放器，我已经能够使用以下SQL：

SELECT BAND.NAME AS Band_Name, KBPLAYER.NAME AS Keyboard_Player
FROM BAND
FULL OUTER JOIN (
    SELECT M.NAME, MO.BID
    FROM MEMBEROF MO, MEMBER M
    WHERE MO.INSTRUMENT='keyboards'
    AND M.MID=MO.MID
    ) KBPLAYER
ON BAND.BID=KBPLAYER.BID
ORDER BY BAND.NAME, KBPLAYER.NAME

以上查询显示该乐队中所有乐队和键盘播放器（如果有）的名称，但我还想为那些没有键盘手的乐队显示“No KeyBoard Players”。我怎样才能做到这一点？如果您需要我提供表格结构的详细信息，请告诉我。

更新：请注意，我无法使用任何SQL3 procedures（COALESCE, CASE, IF..ELSE）。它需要严格遵守SQL3标准。

Answer 1

使用coalesce功能。此函数返回其中第一个非null的参数。例如：

COALESCE(KBPLAYER.NAME,'No KeyBoard Players') AS Keyboard_Player

Answer 2

我决定采用不同的方式，因为我没有使用上述SQL。如果有人建议用上面的SQL设置约束，我将不胜感激。

SELECT 
  band.name AS Band_Name, 'NULL' AS Keyboard_Player
FROM 
  memberof
INNER JOIN 
 member
ON 
  memberof.mid = member.mid 
FULL JOIN 
  band
ON 
  memberof.bid = band.bid 
AND 
  instrument = 'keyboards'

WHERE  
  member.name IS NULL 

UNION

SELECT 
  band.name AS Band_Name, member.name AS Keyboard_Player
FROM 
  memberof
INNER JOIN 
 member
ON 
  memberof.mid = member.mid 
FULL JOIN 
  band
ON 
  memberof.bid = band.bid 
WHERE
  instrument = 'keyboards'

Answer 3

根据你的评论将空字符串替换为某些文本，简单的解决方案是使用如下的case语句。

SELECT BAND.NAME AS Band_Name, 
CASE WHEN KBPLAYER.NAME = '' THEN 'No Player' ELSE KBPLAYER.NAME END AS Keyboard_Player
FROM BAND
FULL OUTER JOIN (
    SELECT M.NAME, MO.BID
    FROM MEMBEROF MO, MEMBER M
    WHERE MO.INSTRUMENT='keyboards'
    AND M.MID=MO.MID
    ) KBPLAYER
ON BAND.BID=KBPLAYER.BID
ORDER BY BAND.NAME, KBPLAYER.NAME

Answer 4

试试这个......

    SELECT BAND.NAME AS Band_Name, 
ISNULL(NULLIF(KBPLAYER.NAME,''),'No KeyBoard Players') AS Keyboard_Player
    FROM BAND
    FULL OUTER JOIN (
        SELECT M.NAME, MO.BID
        FROM MEMBEROF MO, MEMBER M
        WHERE MO.INSTRUMENT='keyboards'
        AND M.MID=MO.MID
        ) KBPLAYER
    ON BAND.BID=KBPLAYER.BID
    ORDER BY BAND.NAME, KBPLAYER.NAME

Answer 5

如果允许使用NVL，则以下情况应该有效。

NVL(KBPLAYER.NAME, 'No KeyBoard Players')

SQL用自己的文本替换NULL值

5 个答案: