嵌套选择中的情况

Question

我无法让 CASE 语句在嵌套选择中工作。我想我已经很接近了，但我无法完全正确地理解语法。到目前为止，我已经尝试过：

SELECT l.*,
Credit = (
CASE WHEN ISNULL(M.POSTCODE,'') <> '' THEN
  sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4)
 ELSE
 sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4) 
 END 
)
FROM live l INNER JOIN master m on m.ClientID = L.ClientID 
WHERE ClientID = 12345

而且：

SELECT l.*,
(SELECT
CASE WHEN ISNULL(M.POSTCODE,'') <> '' THEN
  sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4)
 ELSE
 sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4) 
 END 
) AS Credit
FROM live l INNER JOIN master m on m.ClientID = L.ClientID 
WHERE ClientID = 12345

这似乎与 http 上的 MSDN 示例相匹配://msdn.microsoft.com/en-us/library/ms181765.aspx。我错过了什么吗？

Answer 1

我认为您需要在求和子查询之前添加一些选择。

SELECT l.*,
Credit = (
   CASE WHEN ISNULL(M.POSTCODE,'') <> '' THEN
     (SELECT sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4))
   ELSE
     (SELECT sum(Credit) from Balance cb Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4))
   END 
) 
FROM live l 
    INNER JOIN master m on m.ClientID = L.ClientID 
WHERE ClientID = 12345

您的选择也完全相同，因此实际上不需要案例，除非您希望它们不同。

Answer 2

SELECT l.*,
      CASE 
         WHEN ISNULL(M.POSTCODE,'') <> '' THEN
             (SELECT sum(Credit) 
             from Balance cb 
             Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4))
         ELSE
             (SELECT sum(Credit) 
             from Balance cb 
             Where LEFT(LTrim(cb.AccountHolder),4) LIKE LEFT(LTrim(m.Company),4) )
       END as 'Credit'
FROM live l  INNER JOIN master m 
       on m.ClientID = L.ClientID 
WHERE ClientID = 12345