>>This query
>>

>>select * from myTable where Condition1 OR Condition2
>>

>>is the same as
>>

>>select * from myTable where Condition1
>>UNION
>>select * from myTable where Condition2

>
>Is it really faster?
>
>Also, we need to consider that the select line is very big. So, if I have 1000 primary keys, I would have to repeat that line 1000 times.

No, not necessary. Most likely it will perform the same, but only tests will tell for sure. I saw UNION suggested by Erland Sommarskog on a few occasions.

I am also not sure about your 1000 primary keys - why is it relevant?

In any case, you asked what can be used instead of OR and I gave you the answer.