Saulius Gražulis

> which you can translate to an SQL LIKE query for your backend this way: > > 1. Make these substitutions in ``: > > * `%` -> `\%` >...

> If you agree with that statement; can we perhaps discuss a "ladder" of complexity levels? This is my view: > > 1. Basic operations: STARTS WITH, ENDS WITH, CONTAINS:...

> After researching this, I'll accept that `LIKE` _with_ `ESCAPE` behaves fairly standard across SQL backends, I also find it so. > aside that some add their own pattern extensions......

> Why are you talking about character ranges? I'm talking about LIKE-equivalent (level 2) patterns here as you have described it in your PR I must have meant the most...

After talking with Andrius over the lunch, we came up with an alternative (compromise?) solution: Let's leave just two "complexity levels": - `STARTS/ENDS/CONTAINS` operators _(required)_; - ERE `MATCH` operator _(optional)_....

A Regexp survey: > MySQL uses the extended version to support regular expression pattern-matching operations in SQL statements (https://dev.mysql.com/doc/refman/5.7/en/regexp.html) > MongoDB uses Perl compatible regular expressions (i.e. “PCRE” ) version...

@rartino : just a quick answer to the EREPCRE compatibility question: > But, can you clarify a homework-not-done question: is PCRE a strict superset of functionality of EREs so we...

> I like your latest suggestions for how to support regexes. I see no issue with implementing regex support first and leave a hypothetical level 2 until later. I agree....

https://www.crystallography.net/cod/optimade/references/1000000 https://www.crystallography.net/cod/optimade/structures/2000000 https://www.crystallography.net/cod/optimade/structures?filter=elements+HAS+%22He%22 https://www.crystallography.net/cod/optimade/structures?page_offset=3 NB. Need to check v1.0.0 compliance... :) https://www.crystallography.net/cod/optimade/v0.10.0/references/1000000 The `v1.0.0` is not yet out, so we do not have a: https://www.crystallography.net/cod/optimade/v1/references/1000000 ...

While writing EBNF for the symmetry operation syntax, it occurred to me that what we are describing is a regular language, and so can be defined using a regular expression....