Language Injections Matching

Hello, I've been feeling really stupid trying to add a pretty simple custom language injection. Instead of the default SQL Select Injection (" *SELECT .*FROM .*"), I want to exclude any literal that includes %s. Should be simple enough, but the regex matching behaves very unpredictably and I was unable to find any documentation. I've tried excluding “%” specifically, using [\w], [a-zA-Z0-9_], etc. instead of the .* between select and from, but basically nothing works as expected. 

The only thing I've got working is " *SELECT [a-z_]* FROM .*", but any other expression should work aswell, no? To be clear, [a-z_] works, but [a-zA-Z_] doesn't. What am I missing?

Also: How do escapes work? The \ from \w is removed on save, but \\w doesn't seem to work either.

Thanks.