如何編寫有多個case的where子句？

Question

我有了一個可空參數的存儲過程，而下面是我的查詢

select * 
from table1 
where table1.id = isnull(@id, table1.id) 

現在也有一些特殊的ID我區別對待。我加入另一個表表2像下面

combid id 
1   abc01 
1   abc02 
1   abc03 
2   hig01 
2   hig02 

我不得不更改查詢以滿足下列情況

1. 如果@id爲null，where子句將table1.id = table1.id
2. 如果@id不爲空，
   2.1如果@id存在於表2中，where子句將是table1.id in (select id from table2 where combid in (select combid from table2 where id=@id))
   2.2否則where子句將是table1.id = @id

我試過下面的查詢，但不起作用。

select * from table1 
where (table1.id=@id and not exists(select * from table2 where id=@id) 
or @id is null 
or table1.id in (select id from table2 where combid in (select combid where id=@id)) and exists(select * from table2 where id=@id)) 

如何更改存儲過程的查詢？

Answer 1

SELECT * FROM table1 
WHERE 
    @id IS NULL 
    OR 
    (
     @id IS NOT NULL 
     AND 
     (  
      (
       EXISTS (SELECT * FROM TABLE2 WHERE id = @id) 
       AND 
       table1.id IN (SELECT id FROM table2 WHERE combid in (SELECT combid FROM table2 WHERE id=@id)) 
      ) 
      OR 
      (
       NOT EXISTS (SELECT * FROM TABLE2 WHERE id = @id) 
       AND   
       table1.id = @id 
      ) 
     ) 
    ) 

Answer 2

您可以使用if ... else ...而不是隻寫一條SELECT語句，使用，否則爲您的案例更容易閱讀。

if(@id is null) 
    select * from table1 
else if exists (select 1 from table2 where id = @id) 
    select * from table1 
    where table1.id in 
        (select id from table2 where combid in 
         (select combid from table2 where id=@id) 
       ) 
else 
    select * from table1 where table1.id=@id