帶有兩個函數的條件內連接

Question

我有兩個功能。 我需要根據 BIT 值決定是否加入這兩個。

ON APEL.data_Period_dataination_Lookup_ID = CCEL.data_Period_dataination_Lookup_ID
INNER JOIN  markcommon.GetPredecessordatadataIds() AS PIDS
IF @Combined_Flag=1 
BEGIN
ON PIDS.data_Period_dataination_Identifier = APEL.data_Period_dataination_Identifier
AND PIDS.data_Period_Identifier = APL.data_Period_Identifier
END

基本上

如果 BIT=0 加入 function 1 否則加入 function 2

我嘗試放置一個 IF 子句.. 但它似乎不起作用。 正確的方法是什么？

Answer 1

只需將您的 static 條件添加為連接條件的一部分，並使用LEFT JOIN來確保它適用於缺失的行。 然后，您可以在 select 中使用case表達式來獲取正確的列，例如

SELECT

    CASE WHEN F1.id IS NOT NULL THEN F1.MyColumn ELSE F2.MyColumn END

FROM ...

LEFT JOIN markcommon.Function1() AS F1
  ON @Combined_Cohort = 1
  AND {The rest of the join conditions}

LEFT JOIN markcommon.Function2() AS F2
  ON @Combined_Cohort = 0
  AND {The rest of the join conditions}

Answer 2

我認為您可以只使用LEFT JOIN ：

    ON APEL.data_Period_dataination_Lookup_ID = CCEL.data_Period_dataination_Lookup_ID LEFT JOIN
    markcommon.GetPredecessordatadataIds() PIDS
    ON @Combined_Cohort = 1 AND
       PIDS.data_Period_dataination_Identifier = APEL.data_Period_dataination_Identifier AND
       PIDS.data_Period_Identifier = APL.data_Period_Identifier
. . .
WHERE @Combined_Cohort <> 1 OR PIDS.data_Period_dataination_Identifier IS NOT NULL

Answer 3

您可以按如下方式使用LEFT JOIN ：

APEL.data_Period_dataination_Lookup_ID = CCEL.data_Period_dataination_Lookup_ID
LEFT JOIN  markcommon.GetPredecessordatadataIds() AS PIDS
       ON (@Combined_Flag=1 AND PIDS.data_Period_dataination_Identifier = APEL.data_Period_dataination_Identifier
        AND PIDS.data_Period_Identifier = APL.data_Period_Identifier
        )
LEFT JOIN FUNCTION2() AS PIDS2
       ON (@Combined_Flag=0 AND <<join condition for function 2>>
        )

Answer 4

另請檢查：

SELECT
    IIF(F1.id IS NOT NULL,F1.MyColumn,F2.MyColumn)    
FROM ...

LEFT JOIN markcommon.Function1() AS F1
  ON @Combined_Cohort = 1 
  AND {The rest of the join conditions}

LEFT JOIN markcommon.Function2() AS F2
  ON @Combined_Cohort != 1 
  AND {The rest of the join conditions}