Oracle sql query avoid UNION clause?

Question

I am new to SQL. i am using Oracle10g. i have below query. it has 3 parts and am doing UNION of all three parts. But in every query most of the logic is common except join table. is it possible to avoid UNION and place everything in a single block?

    SELECT DISTINCT e.some_id
         FROM
             main_table e,
             main_table_join_one x     //only change
             where  e.some_id = x.some_id(+)
             and (x.status in('A','I') or x.status is null)
             and e.code='XYZ' and e.second_code in('XYZ','ABC')

             UNION

    SELECT DISTINCT ef.some_id
         FROM
             main_table ef,
             main_table_join_two xf  //only change
             where  ef.some_id = xf.some_id(+)
             and (xf.status in('A','I') or xf.status is null)
             and ef.code='XYZ' and ef.second_code in('XYZ','ABC')

             UNION

    SELECT DISTINCT eff.some_id
         FROM
             main_table eff,
             main_table_join_three xff   //only change
             where  eff.some_id = xff.some_id(+)
             and (xff.status in('A','I') or xff.status is null)
             and eff.code='XYZ' and eff.second_code in('XYZ','ABC')

Thanks!

Answer 1

you can use exists

select distinct e.some_id
  from main_table e
 where e.code = 'XYZ'
   and e.second_code in ('XYZ', 'ABC')
   and (exists (select 0
                  from main_table_join_one x / / only change
                 where x.some_id = e.some_id
                   and (x.status in ('A', 'I') or x.status is null)) 
    or exists
        (select 0
           from main_table_join_two x / / only change
          where x.some_id = e.some_id
            and (x.status in ('A', 'I') or x.status is null))  
    or exists
        (select 0
           from main_table_join_three x / / only change
          where x.some_id = e.some_id
            and (x.status in ('A', 'I') or x.status is null)))

EDITED

fully same result as in topic starter case

select distinct e.some_id
  from main_table e
 where e.code = 'XYZ'
   and e.second_code in ('XYZ', 'ABC')
   and (exists (select 0
                  from main_table_join_one x
                 where x.some_id = e.some_id
                   and x.status in ('A', 'I')) 
    or not exists
        (select 0 from main_table_join_one x where x.some_id = e.some_id) 
    or exists
        (select 0
           from main_table_join_two x
          where x.some_id = e.some_id
            and x.status in ('A', 'I'))
    or not exists
        (select 0 from main_table_join_two x where x.some_id = e.some_id) 
    or exists
        (select 0
           from main_table_join_three x
          where x.some_id = e.some_id
            and x.status in ('A', 'I')) 
    or not exists
        (select 0 from main_table_join_three x where x.some_id = e.some_id))

Answer 2

Why are you using an OUTER JOIN? You are only selecting the main_table.some_id , and the outer joins mean you'll get that regardless of whether there's any matches in the other tables. (Although as Mark Bannister observes, because you've mangeled the outer join syntax you're actually running inner joins).

So you'll get the same result set (assuming you corrected the outer join syntax) if you just run:

SELECT DISTINCT e.some_id
FROM main_table e
where e.code='XYZ' 
and e.second_code in('XYZ','ABC')

Perhaps you've mangled the logic in presenting us with a sanitized test case? Or perhaps you're not clear about the business rules you're supposed to be implementing?

Answer 3

    select distinct ear.RecId,0 Recid,em.EmpCode EmpId,                 
      (em.EmpFirstName+' '+em.EmpMiddleName+' '+em.EmpLastName) as Name,                   
   dm.DeptName as Department,                  
   EAR.AttendType [AttendType],                  

  Convert(varchar,ActualDate,110)  [AttendDate],                  
   EAR.Reason,                      
   ear.StatusOfAdmin Status                      
    from Employeemaster em,                   
   DepartmentMaster dm,                  
   EmpAttenednaceRequest ear,                  
   empAttendanceRequestTransaction eart  

Answer 4

Try this query

 SELECT DISTINCT e.some_id
 FROM
         main_table e,
         main_table_join_one x,
         main_table_join_two xf,
         main_table_join_three xff 
 where e.code='XYZ' and e.second_code in('XYZ','ABC') AND
         ((e.some_id = x.some_id
         and (x.status in('A','I') or x.status is null) 
         OR (ef.some_id = xf.some_id
         and (xf.status in('A','I') or xf.status is null))
         OR (eff.some_id = xff.some_id
         and (xff.status in('A','I') or xff.status is null)))

If ef and eff does not exist

EDITED

 SELECT DISTINCT e.some_id
 FROM
         main_table e,
         main_table_join_one x,
 where e.code='XYZ' and e.second_code in('XYZ','ABC') AND
         e.some_id = x.some_id and
         (x.status in('A','I') or x.status is null);