我遇到了MySQL问题，这是查询：
SELECT JAN.Sales_Phase, JAN.January, FEB.Febuary, MAR.March, APR.April, MAY.May, JUN.June, JUL.July, AUG.August, SEP.September, OCT.October, NOV.November,
DEC.December
FROM (SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS January
FROM MasterTable_TM
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '1')
GROUP BY Sales_Phase) AS JAN LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS Febuary
FROM MasterTable_TM AS MasterTable_TM_1
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '2')
GROUP BY Sales_Phase) AS FEB ON FEB.Sales_Phase = JAN.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS March
FROM MasterTable_TM AS MasterTable_TM_2
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '3')
GROUP BY Sales_Phase) AS MAR ON MAR.Sales_Phase = FEB.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS April
FROM MasterTable_TM AS MasterTable_TM_3
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '4')
GROUP BY Sales_Phase) AS APR ON APR.Sales_Phase = MAR.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS May
FROM MasterTable_TM AS MasterTable_TM_4
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '5')
GROUP BY Sales_Phase) AS MAY ON MAY.Sales_Phase = APR.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS June
FROM MasterTable_TM AS MasterTable_TM_5
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '6')
GROUP BY Sales_Phase) AS JUN ON JUN.Sales_Phase = MAY.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS July
FROM MasterTable_TM AS MasterTable_TM_6
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '7')
GROUP BY Sales_Phase) AS JUL ON JUL.Sales_Phase = JUN.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS August
FROM MasterTable_TM AS MasterTable_TM_7
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '8')
GROUP BY Sales_Phase) AS AUG ON AUG.Sales_Phase = JUL.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS September
FROM MasterTable_TM AS MasterTable_TM_8
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '9')
GROUP BY Sales_Phase) AS SEP ON SEP.Sales_Phase = AUG.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS October
FROM MasterTable_TM AS MasterTable_TM_9
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '10')
GROUP BY Sales_Phase) AS OCT ON OCT.Sales_Phase = SEP.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS November
FROM MasterTable_TM AS MasterTable_TM_10
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '11')
GROUP BY Sales_Phase) AS NOV ON NOV.Sales_Phase = OCT.Sales_Phase LEFT OUTER JOIN
(SELECT Sales_Phase, COALESCE (SUM(PO_Amount_USD), 0) AS December
FROM MasterTable_TM AS MasterTable_TM_11
WHERE (Sales_Phase = 'Credits Card') OR
(Sales_Phase = 'PO Received') AND (PO_Month = '12')
GROUP BY Sales_Phase) AS DEC ON DEC.Sales_Phase = NOV.Sales_Phase
9月和10月内有数据记录，但另一个月没有数据记录。 我试图运行此查询但返回零结果。如果我删除其他月份并且仅在查询中留下9月和10月，则会有结果回馈给我。
如果显示另一个月，即使它是null，怎么办呢？ 使用COALESCE（）函数，但它不起作用。
答案 0 :(得分：1)
你真的不需要那么多的连接来实现数据透视，只需像这样分组：
SELECT Sales_Phase
, SUM(case PO_Month when 1 then PO_Amount_USD else 0 end) AS January
, SUM(case PO_Month when 2 then PO_Amount_USD else 0 end) AS Febuary
, SUM(case PO_Month when 3 then PO_Amount_USD else 0 end) AS March
, SUM(case PO_Month when 4 then PO_Amount_USD else 0 end) AS April
, SUM(case PO_Month when 5 then PO_Amount_USD else 0 end) AS May
, SUM(case PO_Month when 6 then PO_Amount_USD else 0 end) AS June
, SUM(case PO_Month when 7 then PO_Amount_USD else 0 end) AS July
, SUM(case PO_Month when 8 then PO_Amount_USD else 0 end) AS August
, SUM(case PO_Month when 9 then PO_Amount_USD else 0 end) AS September
, SUM(case PO_Month when 10 then PO_Amount_USD else 0 end) AS October
, SUM(case PO_Month when 11 then PO_Amount_USD else 0 end) AS November
, SUM(case PO_Month when 12 then PO_Amount_USD else 0 end) AS December
FROM MasterTable_TM
WHERE (Sales_Phase = 'Credits Card')
OR (Sales_Phase = 'PO Received')
AND (PO_Month between '1' and '12') -- these conditions do really make no sense, but leave it as the original sample code
GROUP BY Sales_Phase
您的查询中有两个问题：
(Sales_Phase = 'Credits Card') OR (Sales_Phase = 'PO Received') AND (PO_Month = '1')如此令人困惑，如果Sales_Phase ='Credits Card'，您想要从所有月份返回数据吗？ AND的优先级高于OR