How to set SQL condition precedence for two different conditions

 

I'm having two different tables ' TABLE1 ' and ' TABLE2 '. Both of these tables have same column name - ' IS_PDF '.

RE TABLE1.IS_PDF value, I retrieved the required details using select statement where I added where clause like below. 

select * from TABLE1 where TABLE1.IS_PDF = 'Y';

Similarly, I can get the values for TABLE2 as well where TABLE2.IS_PDF = 'Y'

Now, my task is to have one select statement to get the details from both tables ' TABLE1 ' and ' TABLE2 ' by setting a precedence on below condition # 1 .

  • If TABLE1.IS_PDF = 'Y' , return records matching same condition.
  • If TABLE1.IS_PDF = 'N' but TABLE2.IS_PDF = 'Y' then return records matching same condition.
  • If both have IS_PDF = 'N', return nothing.

    • I used below Select statement but getting Above conditions # 1 and 2 at the same time only. 

    select * from TABLE1, TABLE2
where
(TABLE1.IS_PDF = 'Y') or (TABLE2.IS_PDF = 'Y' and TABLE1.IS_PDF = 'N' )

    Please guide on the same. Thanks

    You seem to want something like this: 

    select t1.*
from table1 t1
where t1.is_pdf = 'Y'
union all
select t2.*
from table2 t2
where t2.is_pdf = 'Y' and
      not exists (select 1 from table1 t1 where t1.is_pdf = 'Y' and t1.?? = t2.??);

    The ?? represents the column(s) used for matching between the two tables.

    Thanks for the quick response.

    Sample code- 

    select TABLE1.IS_PDF, TABLE2.IS_PDF, TABLE1.ID, TABLE1.GLOBAL_ID, TABLE1.title, 
from TABLE1, TABLE2
where TABLE1.USER_ID = 82340
and TABLE1.NAME = 'INDIA'
and (TABLE1.IS_PDF = 'Y') or (TABLE2.IS_PDF = 'Y' and TABLE1.IS_PDF = 'N' )

    I need to set a precedence on below condition # 1. If condition # 1 meets, it's fine. Otherwise go for #2 then #3.

  • If TABLE1.IS_PDF = 'Y', return records matching same condition.
  • If TABLE1.IS_PDF = 'N' but TABLE2.IS_PDF = 'Y' then return records matching same condition.
  • If both have IS_PDF = 'N', return nothing.
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