mysql, space equals empty string

Question

Just took me 2 hours to troubleshoot an issue on my backend.

Cause was that of empty string being equal to space:

SELECT ' ' = '';
-> 1

SELECT STRCMP(' ', '');
-> 0 /* means equal */

Interestingly enough,

SELECT '' REGEXP '[ ]';
-> 0
SELECT '' REGEXP ' ';
-> 0
SELECT ' ' REGEXP ' ';
-> 1

Can I prevent this? Is it a setting?

Answer 1

The reason this fails is explained in the docs here http://dev.mysql.com/doc/refman/5.0/en/char.html:

Values in CHAR and VARCHAR columns are sorted and compared according to the character set collation assigned to the column.

All MySQL collations are of type PADSPACE. This means that all CHAR, VARCHAR, and TEXT values in MySQL are compared without regard to any trailing spaces. “Comparison” in this context does not include the LIKE pattern-matching operator, for which trailing spaces are significant.

One way to work around this would be to cast as BINARY

SELECT BINARY '' = ' ';
0

You can also use LIKE:

SELECT '' LIKE ' ';
0