Regular expressions

The regex engine behind regexp_matches, regexp_extract and regexp_replace is a subset, sized for the patterns SQL actually carries rather than for a dependency. It supports ^ $ . |, character classes with ranges and negation, capturing and non-capturing groups, the escapes \d \w \s (and their negations), the quantifiers * + ? and counted {n} {n,} {n,m} — each greedy, or lazy with a ? suffix (*?, {2,4}?), and \n \t \r and an escaped punctuation character (\., \$). Lookaround, backreferences (\1) and every other letter or digit escape (\b, \A) are rejected at compile time rather than read as literal characters, so an unsupported pattern is an error and never a silently wrong match.