Hex characters in regexp matching in mysql

This matches too:

SELECT CONVERT('a' USING BINARY) REGEXP '[1-\x]'

The reason is that \x is interpeted as x and a comes between 1 and x. The rest of your regex is just ordinary characters that aren't relevant here because they're already inside the [1-x] range.

SELECT CONVERT('0' USING BINARY) REGEXP '[\x61-\x61]' -- Fails, because 0 < 1.
SELECT CONVERT('1' USING BINARY) REGEXP '[\x61-\x61]' -- Succeeds: inside [1-x].
SELECT CONVERT('2' USING BINARY) REGEXP '[\x61-\x61]' -- Succeeds: inside [1-x].
...
SELECT CONVERT('w' USING BINARY) REGEXP '[\x61-\x61]' -- Succeeds: inside [1-x].
SELECT CONVERT('x' USING BINARY) REGEXP '[\x61-\x61]' -- Succeeds: inside [1-x].
SELECT CONVERT('y' USING BINARY) REGEXP '[\x61-\x61]' -- Fails, because y > x.

I'm not sure what you're trying to achieve, but if you want hex characters, you can use the hex function:

SELECT HEX('a')
61

to write a regexp like [\x61-\x65] in mysql, you can use hex values inside a concat:

SELECT CONVERT('a' USING BINARY) REGEXP CONCAT('[', 0x61, '-', 0x65, ']')

Lol... based on the above you can just use the print characters. That worked for me. I wanted to make it match characters not on a USA keyboard and the following expression works on MySQL 5.1:

[^ -~]

That will do the same thing as

[^\x20-\x7E]