No, it's a result of the collation you use. I'm guessing that the defauult collation for the column you tested this on is case sensitive. In most case sensitive collations, capitals sort first. So A comes first, then a, then B, then b, etc. That's why 'A' is included in [A-Z] but not in [a-z] - because the capital A comes before the small a, which is the starting point for the second LIKE patters.