Question

(dynamic query…)

select * from myTable where

(   <--- 

 @param1 IS NULL
                  OR (
                         param1 IN 
                                           ( 
                                              SELECT item
                                              FROM   blabla1
                                           )
                     )
)   <---
and
(   <---

 @param2 IS NULL
                  OR (
                         param2  IN 
                                           ( 
                                              SELECT item
                                              FROM   blabla2
                                           )
                     )
)   <---

question :

look at the parenthesis marked with <---.

Can I remove them ( without impacting the logic here ) ?

Answer 1

No. you need those but you can remove the ones around the IN statement.

select * 
from myTable
where
  (@param1 IS NULL OR @param1 IN (SELECT item FROM blabla1))
  and 
  (@param2 IS NULL OR @param2 IN (SELECT item FROM blabla2))

If you remove the ones you asked about you would have a query that works like this

select * 
from myTable
where
  param1 IS NULL
  OR
  (param1 IN (SELECT item FROM blabla1)) and param2 IS NULL 
  OR
  (param2 IN (SELECT item FROM blabla2))