performance degrades if one argument in "In Clause" ?

[aiyaonline]

I like to know if the following makes any performance issue.

select field_1 from table_1 where country ='USA';
(or)
select field_1 from table_1 where country in ('USA');

The reason behind is:

(a) For some scenario, country can only be 'USA'.
(b) And for some other, country can be 'USA' or 'EUR' or 'AUS'.

So, I am in a fix where i can use "In" clause in (a), so that my dynamic query becomes simpler and generic for both (a) and (b). Otherwise, if having one argument in "IN" clause degrades the performance, then i have to make for two dynamic queries, one using equality and another using "IN".

Appreciate your comments on this.

[michaelb]

I like to know if the following makes any performance issue.

select field_1 from table_1 where country ='USA';
(or)
select field_1 from table_1 where country in ('USA');

Chances are the query optimizer converts "where country in ('USA')" into "where country = 'USA'" anyway.
In any case you can probably use the EXPLAIN on your query to get this and other performance related information.