Help with Corelated sub-query

Question

I am trying to improve this query? Is there a better way to write the query and get the same results. I hate the fact that I am querying a table 3 times.
Select statement
WITH t1 AS
     (SELECT 101 AS ID
           , 1 AS a
           , NULL AS b
           , 5 AS c
        FROM DUAL
      UNION ALL
      SELECT 102
           , NULL
           , 2
           , 5
        FROM DUAL
      UNION ALL
      SELECT 101
           , 3
           , 5
           , 7
        FROM DUAL
      UNION ALL
      SELECT 101
           , 1
           , NULL
           , NULL
        FROM DUAL)
   , t2 AS
     (SELECT 101 AS ID
           , 1 AS x
        FROM DUAL
      UNION ALL
      SELECT 101
           , 5
        FROM DUAL
      UNION ALL
      SELECT 102
           , 5
        FROM DUAL
      UNION ALL
      SELECT 102
           , 2
        FROM DUAL)
SELECT *
  FROM t1
WHERE t1.ID = 101
   AND (   t1.a IS NULL
        OR t1.a IN (SELECT t2.x
                      FROM t2
                     WHERE t2.ID = t1.ID))
   AND (   t1.b IS NULL
        OR t1.b IN (SELECT t2.x
                      FROM t2
                     WHERE t2.ID = t1.ID))
   AND (   t1.c IS NULL
        OR t1.c IN (SELECT t2.x
                      FROM t2
                     WHERE t2.ID = t1.ID))Output:
        ID          A          B          C
       101          1                     5
       101          1                      -- Thanks

Answer 1

This is an interesting question.
WITH t1 AS
     (SELECT 101 AS ID, 1 AS ColA, NULL AS ColB, 5 AS ColC FROM DUAL UNION ALL
      SELECT 102, NULL, 2, 5 FROM DUAL UNION ALL
      SELECT 101, 3, 5, 7 FROM DUAL UNION ALL
      SELECT 101, 5,99,99 FROM DUAL UNION ALL
      SELECT 101, 1, NULL, NULL FROM DUAL)
   , t2 AS
     (SELECT 101 AS ID , 1 AS ColX FROM DUAL UNION ALL
      SELECT 101 , 5 FROM DUAL UNION ALL
      SELECT 102 , 5 FROM DUAL UNION ALL
      SELECT 102 , 2 FROM DUAL UNION ALL
      SELECT 101 , 3 FROM DUAL UNION ALL
      SELECT 101 , 5 FROM DUAL UNION ALL
      SELECT 101 , 7 FROM DUAL)
select *
  from t1 a
where ID = 101
   and exists(select 1
                from t2 b
               where b.ID = a.ID
              having (a.ColA is null or max(case when b.ColX = a.ColA then 1 else 0 end) = 1)
                 and (a.ColB is null or max(case when b.ColX = a.ColB then 1 else 0 end) = 1)
                 and (a.ColC is null or max(case when b.ColX = a.ColC then 1 else 0 end) = 1));
ID  ColA  ColB  ColC
101     1  null     5
101     3     5     7
101     1  null  nullFurthermore,
We can use below alternative solution.
Below alternative solution is used Boolean arithmetic (http://www.allaboutcircuits.com/vol_4/chpt_7/2.html)
WITH t1 AS
     (SELECT 101 AS ID, 1 AS ColA, NULL AS ColB, 5 AS ColC FROM DUAL UNION ALL
      SELECT 102, NULL, 2, 5 FROM DUAL UNION ALL
      SELECT 101, 3, 5, 7 FROM DUAL UNION ALL
      SELECT 101, 5,99,99 FROM DUAL UNION ALL
      SELECT 101, 1, NULL, NULL FROM DUAL)
   , t2 AS
     (SELECT 101 AS ID , 1 AS ColX FROM DUAL UNION ALL
      SELECT 101 , 5 FROM DUAL UNION ALL
      SELECT 102 , 5 FROM DUAL UNION ALL
      SELECT 102 , 2 FROM DUAL UNION ALL
      SELECT 101 , 3 FROM DUAL UNION ALL
      SELECT 101 , 5 FROM DUAL UNION ALL
      SELECT 101 , 7 FROM DUAL)
select *
  from t1 a
where ID = 101
   and exists(select 1
                from t2 b
               where b.ID = a.ID
              having max(case when b.ColX = a.ColA or a.ColA is null then 1 else 0 end)
                   * max(case when b.ColX = a.ColB or a.ColB is null then 1 else 0 end)
                   * max(case when b.ColX = a.ColC or a.ColC is null then 1 else 0 end) = 1);This thread is dealt logic which is "max(case when P(X) then 1 else 0 end) = 1" is for some X:P(X).
And this thread deals alike question.
Re: Select only records with same Id
I mentioned alike logic in this thread.
Re: Newbie: Simple select with 'IN ALL'
I recommend these articles.
http://www.dbazine.com/ofinterest/oi-articles/celko5
http://www.dbazine.com/ofinterest/oi-articles/celko18