Question

我正在尝试使用if else案例基于两个选择条件加入数据。我有一个汇率表（dbo.DATA_EXCHANGE_RATE），一个有年（dbo.DATA_EXCHANGE_RATE.YEAR_OBJ_REF），另一个有货币（dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF）。如果货币是欧元，我想仅根据货币选择我的汇率，否则根据年份和货币。我拥有的是

select dbo.DATA_EXCHANGE_RATE.EXCHANGE_RATE_CAPTION
from dbo.DATA_EXCHANGE_RATE
inner join dbo.measures
on(CASE WHEN dbo.measures.CURRECY_OBJ_REF =
         (select DATA_ID from dbo.DATA_CURRENCY where CURRENCY_CAPTION = 'T-EUR')
   THEN
      dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF
   ELSE
      dbo.DATA_EXCHANGE_RATE.YEAR_OBJ_REF = dbo.measures.YEAR_OBJ_REF
      and dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF
   END)

但这会引发错误：

  Failed!
Incorrect syntax near '='

Answer 1

我认为以下查询维护您的预期逻辑，减去语法错误：

SELECT dbo.DATA_EXCHANGE_RATE.EXCHANGE_RATE_CAPTION
FROM dbo.DATA_EXCHANGE_RATE t1
INNER JOIN dbo.measures t2
ON
(
    dbo.measures.CURRECY_OBJ_REF = (select DATA_ID from dbo.DATA_CURRENCY
                                    where CURRENCY_CAPTION = 'T-EUR')      AND
    t1.CURRECY_OBJ_REF = t2.CURRECY_OBJ_REF
)
OR
(
    dbo.measures.CURRECY_OBJ_REF <> (select DATA_ID from dbo.DATA_CURRENCY
                                     where CURRENCY_CAPTION = 'T-EUR')     AND
    t1.YEAR_OBJ_REF = t2.YEAR_OBJ_REF        AND
    t1.CURRECY_OBJ_REF = t2.CURRECY_OBJ_REF
)

我不喜欢将子查询放入ON子句，因为它感觉很奇怪。我怀疑如果我们要查看您的数据，我们可能会改进此查询。

Answer 2

CASE在过程语言中不像if那样工作，它返回一个原子值。它不能以这种方式用于程序流程。您想要的是AND和OR：

select      DER.EXCHANGE_RATE_CAPTION
FROM        dbo.DATA_EXCHANGE_RATE DER
inner join  dbo.measures M
        ON  (
                    M.CURRECY_OBJ_REF = (SELECT DATA_ID from dbo.DATA_CURRENCY where CURRENCY_CAPTION = 'T-EUR')
                AND DER.CURRECY_OBJ_REF = M.CURRECY_OBJ_REF
            )
        OR  (
                    M.CURRECY_OBJ_REF <> (SELECT DATA_ID from dbo.DATA_CURRENCY where CURRENCY_CAPTION = 'T-EUR')
                AND DER.YEAR_OBJ_REF = M.YEAR_OBJ_REF
                AND DER.CURRECY_OBJ_REF = M.CURRECY_OBJ_REF
            )

我还使用了别名来提高可读性。

Answer 3

＆＃13;

Declare @Query as nvarchar(max) = 'select dbo.DATA_EXCHANGE_RATE.EXCHANGE_RATE_CAPTION
from dbo.DATA_EXCHANGE_RATE
                     inner join dbo.measures
on (CASE WHEN dbo.measures.CURRECY_OBJ_REF =(select DATA_ID from dbo.DATA_CURRENCY where CURRENCY_CAPTION = ''T-EUR'')
   THEN
      dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF
   ELSE
      dbo.DATA_EXCHANGE_RATE.YEAR_OBJ_REF = dbo.measures.YEAR_OBJ_REF
      and dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF
   END)'

   EXEC SP_EXECUTESQL @Query

＆＃13;

Answer 4

将其替换为OR表达式

declare @EURO int;
select @EURO = DATA_ID from dbo.DATA_CURRENCY where CURRENCY_CAPTION = 'T-EUR';

select dbo.DATA_EXCHANGE_RATE.EXCHANGE_RATE_CAPTION
from dbo.DATA_EXCHANGE_RATE
      inner join dbo.measures on (dbo.measures.CURRECY_OBJ_REF = @EURO and dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF) or
                                 (dbo.measures.CURRECY_OBJ_REF <> @EURO and dbo.DATA_EXCHANGE_RATE.YEAR_OBJ_REF = dbo.measures.YEAR_OBJ_REF and dbo.DATA_EXCHANGE_RATE.CURRECY_OBJ_REF = dbo.measures.CURRECY_OBJ_REF);

SQL IF ELSE for Inner join with linked dependency

4 个答案: