Is there a performance difference between BETWEEN and IN with MySQL or in SQL in general?

BETWEEN should outperform IN in this case (but do measure and check execution plans, too!), especially as n grows and as statistics are still accurate. Let's assume:

• m is the size of your table
• n is the size of your range

Index can be used (n is tiny compared to m)

• In theory, BETWEEN can be implemented with a single "range scan" (Oracle speak) on the primary key index, and then traverse at most n index leaf nodes. The complexity will be O(n + log m)

• IN is usually implemented as a series (loop) of n "range scans" on the primary key index. With m being the size of the table, the complexity will always be O(n * log m) ... which is always worse (neglibile for very small tables m or very small ranges n)

Index cannot be used (n is a significant portion of m)

In any case, you'll get a full table scan and evaluate the predicate on each row:

• BETWEEN needs to evaluate two predicates: One for the lower and one for the upper bound. The complexity is O(m)

• IN needs to evaluate at most n predicates. The complexity is O(m * n) ... which is again always worse, or perhaps O(m) if the database can optimise the IN list to be a hashmap, rather than a list of predicates.

a between b and c is a macro that expands to b <= a and a <= c.

a in (b,c,d) is a macro that expands to a=b or a=c or a=d.

Assuming your n and nk are integer, both should end up meaning the same. The between variant should be much faster because it's only two compares, versus nk - n compares for the in variant.