Confluence 2.2.9 does not work with MySQL version prior to 4.1

A space cannot be deleted. The problem is that Label.hbm.xml -> confluence.label_unused uses a sub select (aka sub query). Sub selects have been introduced in MySQL version 4.1.

Fix: Rewrite the statement to use a LEFT JOIN:

select distinct

from LABEL l LEFT JOIN CONTENT_LABEL lc ON l.LABELID = lc.LABELID where lc.LABELID IS NULL

BTW: Regarding to http://confluence.atlassian.com/display/DOC/Confluence+Installation+Guide MySQL version 3.2 is supported.