Regex to SQL Server LIKE / PATINDEX translator

SQL Server does not speak regex in LIKE. It speaks %, _, [] and [^]. If you think in ^, $ and .*, this writes the LIKE for the simple cases and tells you when it cannot.

Python people type ^[A-Z].*co.uk$ and expect it to work. In T-SQL that is closer to LIKE '[A-Z]%co.uk'. Character classes map. Lookaheads, groups and \d do not — use PATINDEX for a few of those, or do it in the app.

A leading % cannot use a normal index well. See LIKE.