Performance question: Union vs OR

Hi Toby,

Can you throw some light on how the performance of the UNION operator
compares with using an OR? I am looking for a generic recommendation on the
circumstances under which use one or the other is preferable. Specifically,
we can say

select <select clause> from <table list> where <condition1>
union
select <select clause> from <table list> where <condition2>


or we can say

select <select clause> from <table list> where <condition1> or <condition2>


My questions:
- Is there any reason to prefer one form over the other? 
- Is there any impact on performance if either of these structures is used in
a subquery?


Thanks in advance.


M. A. Sridhar


		
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