Difference Between [A-Z] and [[:upper:]] in MySQL REGEXP
In MySQL REGEXP, [A-Z] and [[:upper:]] both match uppercase letters, but there are subtle differences in behavior depending on character sets and locale.
[A-Z]: Matches only the ASCII uppercase letters from A to Z. It does not account for letters with accents or uppercase letters in non-ASCII character sets.
[[:upper:]]: This is a POSIX character class that matches all uppercase letters according to the current locale, including accented letters or other uppercase letters outside the basic ASCII range.
Portability:
[[:upper:]]is generally more portable and locale-aware, making it safer for internationalized applications.Usage in Patterns: Both can be used with quantifiers and anchors, e.g.,
^[A-Z]+$or^[[:upper:]]+$to match strings consisting entirely of uppercase letters.
In short, [A-Z] is limited to standard ASCII, while [[:upper:]] adapts to the locale and supports a wider range of uppercase characters.