Thanks for the report.

Alexander Barkov,
I suppose it's a PCRE limitation, but the replication failure is very unfortunate. Is there anything we can do about it? Maybe a non-default mode or a new version which allows the syntax?

The old Henry Spencer regex library supported a number of character names:
https://mariadb.com/kb/en/mariadb/documentation/functions-and-operators/string-functions/regular-expressions-functions/regular-expressions-overview/#character-names
This was a non-standard, non-POSIX extension in the old library.

In POSIX regex the syntax '[[.xxx.]]' is reserved for collating elements.
For some reasons, Henry Spencer reused the same syntax for its character names extension.

PCRE does not support collating elements yet (but I guess it will in the future).
Currently PCRE only recognizes this syntax and just returns an error that you can see.

There is a number of workarounds possible:

For space:

SELECT ' ' REGEXP ' ';
SELECT ' ' REGEXP '[ ]';
SELECT ' ' REGEXP '[[:space:]]';
SELECT ' ' REGEXP '\\{20}';
SELECT ' ' REGEXP '\\x{20}';

For dot:

SELECT '.' REGEXP '[.]';
SELECT '.' REGEXP '\\.';
SELECT '.' REGEXP '\\x2E';
SELECT '.' REGEXP '\\x{2E}';

How difficult would it be to change your application to use these workarounds?

These two are POSIX compliant and are supported by both libraries:

SELECT ' ' REGEXP ' ';
SELECT '.' REGEXP '[.]';

Fortunately it will not be too difficult to change in the instance where it is causing problems.

Thanks. I reported the issue to the PCRE team. Changing priority to minor for now.
We'll escalate the bug if we have more related problems reported.

Same issue with a module for a shopping cart. Currently looking into whether or not this can be easily swapped out in the code, although since the module isn't developed internally, that's likely not going to be an all too easy task.

Would appreciate a fix for this issue.

Same issue with a module for a shopping cart. Currently looking into whether or not this can be easily swapped out in the code, although since the module isn't developed internally, that's likely not going to be an all too easy task.

Would appreciate a fix for this issue.