Requête imbriquée t-sql avec sélection interne définie conditionnellement

Question

J'ai besoin d'une requête imbriquée, mais avec le sql de sélection interne défini conditionnellement.

Cela ne fonctionne pas:

SELECT inner.a, inner.b, t4.c FROM 
CASE 
    WHEN (@Param1 = 1) THEN 
    (SELECT t1.col1 AS a , t2.col2 AS b 
     FROM Table1 t1 
     INNER JOIN Table2 t2 ON t2.pk = t1.fk2) AS inner 
    WHEN (@Param2 = 2) THEN 
    (SELECT t1.col1 AS a , t3.col3 as b 
    FROM Table1 t1 
    LEFT JOIN Table3 t3 ON t3.pk = t1.fk3) AS inner 
END 
LEFT JOIN Table4 t4 ON t4.pk = inner.b 
WHERE inner.a = @Param1 

Answer 1

SELECT inner1.a, inner1.b, outer1.c 
FROM (SELECT t1.col1 AS a , t2.col2 AS b 
     FROM Table1 t1 
     INNER JOIN Table2 t2 ON t2.pk = t1.fk2) AS inner1 
    LEFT JOIN Table4 t4 ON t4.pk = inner1.b 
WHERE @Param1=1 
    AND inner1.a = @Param1 


UNION ALL 

SELECT inner1.a, inner1.b, outer1.c 
FROM (SELECT t1.col1 AS a , t3.col3 as b 
    FROM Table1 t1 
    LEFT JOIN Table3 t3 ON t3.pk = t1.fk3) AS inner1 
LEFT JOIN Table4 t4 ON t4.pk = inner1.b 
WHERE @Param2 =2 
    inner1.a = @Param1 

Answer 2

Essayez ceci:

SELECT InnerTable.a, InnerTable.b, t4.c 
FROM ( SELECT t1.col1 AS a, t2.col2 AS b 
      FROM Table1 t1 INNER JOIN 
        Table2 t2 ON t2.pk = t1.fk2 
      WHERE @Param1 = 1 

      UNION 

      SELECT t1.col1 AS a, t3.col3 AS b 
      FROM Table1 t1 LEFT JOIN 
        Table3 t3 ON t3.pk = t1.fk3 
      WHERE @Param2 = 2 
     ) AS InnerTable 
     LEFT JOIN Table4 t4 ON t4.pk = InnerTable.b 
WHERE InnerTable.a = @Param1 

Answer 3

vous ne pouvez pas utiliser comme cela, utilisez dynamic query pour cette chaîne et exécuter

add où condition aussi dynamiquement aussi et colonne si vous voulez.

comme

DECLARE @SelectStatement NVARCHAR(2000) 

DECLARE @FullStatement NVARCHAR(4000) 

SET @SelectStatement = 'SELECT TOP 5 * FROM SalesHistory ' 

SET @FullStatement = @SelectStatement + ISNULL(@WhereClause,'') 

PRINT @FullStatement 

EXECUTE sp_executesql @FullStatement