From Online Manual
Description: Tells SMF whether the database is case sensitive (PostgreSQL and SQlite) or not (MySQL). Shall not be called as a function, but used a boolean.
Return: True if the database is case sensitive false otherwise.
// Get the case of the columns right - but only if we need to as things like MySQL will go slow needlessly otherwise. $member_name = $smcFunc['db_case_sensitive'] ? 'LOWER(member_name)' : 'member_name'