Using constant expression in query

Question

When I write a query, if I use a bind variable that could be null as for example:
select *
from table
where :variable is null or column = :variable
the performance drops significantly.
I can't find any reason, so if you can help me...
I also tried something simpler, and something I thought it shoud be faster.
select *
from table
where 1=1 or column = :variable
this query should return all the table, since 1=1 is allways true. It should be easier to evaluate, since it's the same as before, but it does not need to bind the variable. It takes five times longer than before.
What I am looking for is to understand what the database does when I run this queries.
Thankyou very much
Edited by: user4823534 on 27-abr-2010 9:16

Answer 1

I think I didn't explain myself.
I have several very complex querys that use bind variables as optional parameters.
What I noticed is that it's much slower (100 times maybe) to have a constant expression which is true in an or than evaluating something else. For example
select * from table where :a is null or column1 in (select column1 from table2 where a = :a) should be faster than
select * from table where column1 in (select column1 from table2 where a = :a) since the last one has to evaluate the in clause, and the first one is allways true.
Thankyou for your patience and sorry for my bad english.