Need some Info and help.

Question

Dear Friends,
I have two selects running something like this:
select <column-names> from <table-names> where <conditions>
union
select <column-names> from <table-names> where <conditions>.
there are three outer-join conditions in the first select and
three outer joins in the second like:
c=l(+)[in the first select]
d=m(+)
e=n(+)
and
f=l(+) [in the second select]
g=m(+)
h=n(+)
The result here generates 52 rows which is correct.
Now the case is that I am removing the union clause from the above SQL
and converting it like this.
select <column-names[1]>+<column-names[2]> from <table-names[1]>+<table-names[2]> where <conditions[1]>+<conditions[2]>
but i get the error:
same table cannot be outerjoined to two tables in the same query because i now have this
in the new query :
c=l(+)[from the first select]
d=m(+)
e=n(+)
f=l(+) [from the second select]
g=m(+)
h=n(+)
if I remove the join like:
c=l[from the first select]
d=m
e=n
f=l(+) [from the second select]
g=m(+)
h=n(+)
the query executes but results into 160 rows too much of unneeded redundancy, which is wrong.
My question is that:"Is there any way to do this? I mean to remove the union and combine the two selects into one without affecting the result of the Query which should be 52 rows only (while not affecting the joins I think this should also be the case)".
Need your suggestions.
Thanks,
Vishal

Answer 1

The union set operator performs a sort and deletes duplicates as a part of its definition.
If your revised query gives you the correct results only with duplicate rows then a select distinct may be all you need.
The cost of the sort and duplicate delete operation will affect your query performance but as the output result set is fairly small I do not think it will make much of a difference.
HTH -- Mark D Powell --