We implement: - [x] `regexp` (for the operator) - [x] `regexp_like` (for compatibility) - [x] `regexp_substr` - [x] `regexp_replace` [Postgres](https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP), Oracle have also: - [x] `regexp_count` - [x] `regexp_instr`
