Report with multiplying columns and WITH clause

Question

Hello
I saw sth strange in my report. I assume that it could happens very often.
I have report with few columns which two of them ar most complicated (many joins subqueries aggreagations on joined values etc.) These two columns (i.e C3,C4) should be multiplied (C3*C4).
When i do pure report without multiplying only columns C1,C2,C3,C4 everything is ok - duration about 15 sec. but... when I put next column on report which multiply these columns (in Answers C5=C3*C4)
I wait 3-4 minutes and my database hungs :(. After investigation I saw that in first case to databese goes pure "SELECT" statement it means:
"Select ... as C1, ... as C2, max(...) as C3, sum(xxx)... C4 from yyy,sss,ttt WHERE aaa"
but in second case BI uses WITH clause it means:
WITH SAWITH0 AS
( Select ... as C1, ... as C2, max(...) as C3, sum(xxx)... C4 from yyy,sss,ttt WHERE aaa )
SELECT SAWITH0.C1 as C1,
SAWITH0.C2 as C2,
     SAWITH0.C3 as C3,
     SAWITH0.C4 as C4,
     SAWITH0.C3*SAWITH0.C4 as C5 FROM SSS
and this statement is long runninq query and kills my database :(.
I checked that SQL like this:
Select ... as C1, ... as C2, max(...) as C3, sum(xxx)... C4, max(...)*sum(xxx)... As C5 from yyy,sss,ttt WHERE aaa" -
runs few times faster than that above
I know that I can do this multiply in business model layer but sometimes users can multiply(or other operations) on columns in reports without my knowledge and it kills my db :(. Where is bug? Why SQLs with WITH clause takes so much db time?
Thank you for each kind of help

Answer 1

WITH clause or Subquery Factoring allows the set of data to be reused multiple times within the SQL. Oracle will usually materialize the data into a temporary table (you will see it if you take an explain plan of the SQL).
I would be surprised if it was the actual WITH clause that was causing the performance issue, however you can test this by turning the WITH clause feature off. Go to the Physical model, right mouse click on your Database > Properties > Features Tab, scroll down to WITH_CLAUSE_SUPPORTED and switch it off.
I'd be interested to know if you do see actual improvement.
Good Luck.