Optimisation, using of one subquery several times,

Question

Hi,
is it possible to optimise such query?
select * from
(select count(*) as count1 from table where a=1) e1,
(select count(*) as count2 from table where a=1 and b=1) e2,
(select count(*) as count3 from table where a=1 and b=1 and c=1) e3,
(select count(*) as count4 from table where a=1 and b=1 and c=1 and d=1) e4
The subquery (select count(*) as count1 from table where a=1) is used and executed 4 times?
Thanks in advance!!!!!!

Answer 1

I think you are both speaking "generally". And generally speaking you might be right sometimes.
But in this case, the case of the question of the original poster, there should be no doubt which is faster by looking at the execution plan. The plan as shown in the explain plan is the plan that gets executed here. There is no bind variable peeking taking place, there are no rows being added or deleted between the times of analyze and execution. So what you see is what you get here.
To help cdkumar convince:
SQL> select count(case when a=1 then a end) e1
  2       , count(case when a=1 and b=1 then a end) e2
  3       , count(case when a=1 and b=1 and c=1 then a end) e3
  4       , count(case when a=1 and b=1 and c=1 and d=1 then a end) e4
  5    from mytable
  6  /
        E1         E2         E3         E4
    500005     400004     300003     200002
1 rij is geselecteerd.
Verstreken: 00:00:01.06
Uitvoeringspan
   0      SELECT STATEMENT Optimizer=CHOOSE
   1    0   SORT (AGGREGATE)
   2    1     TABLE ACCESS (FULL) OF 'MYTABLE'
SQL> with samp_a as
  2  (select * from mytable where a = 1),
  3  samp_b as
  4  (select * from samp_a where b = 1),
  5  samp_c as
  6  (select * from samp_b where c = 1),
  7  samp_d as
  8  (select * from samp_c where d = 1)
  9  select
10  (select count(1) from samp_a) a_cnt,
11  (select count(1) from samp_b) b_cnt,
12  (select count(1) from samp_c) c_cnt,
13  (select count(1) from samp_d) d_cnt
14  from dual
15  /
     A_CNT      B_CNT      C_CNT      D_CNT
    500005     400004     300003     200002
1 rij is geselecteerd.
Verstreken: 00:00:09.02
Uitvoeringspan
   0      SELECT STATEMENT Optimizer=CHOOSE
   1    0   SORT (AGGREGATE)
   2    1     VIEW
   3    2       TABLE ACCESS (FULL) OF 'SYS_TEMP_0FD9D69EB_694E3998'
   4    0   SORT (AGGREGATE)
   5    4     VIEW
   6    5       TABLE ACCESS (FULL) OF 'SYS_TEMP_0FD9D69EC_694E3998'
   7    0   SORT (AGGREGATE)
   8    7     VIEW
   9    8       TABLE ACCESS (FULL) OF 'SYS_TEMP_0FD9D69ED_694E3998'
  10    0   SORT (AGGREGATE)
  11   10     VIEW
  12   11       TABLE ACCESS (FULL) OF 'SYS_TEMP_0FD9D69ED_694E3998'
  13   16     RECURSIVE EXECUTION OF 'SYS_LE_16_0'
  14   16     RECURSIVE EXECUTION OF 'SYS_LE_16_1'
  15   16     RECURSIVE EXECUTION OF 'SYS_LE_16_2'
  16    0   TEMP TABLE TRANSFORMATION
  17   16     TABLE ACCESS (FULL) OF 'DUAL'Regards,
Rob.