This bug will surface when using the ORM and adding an join to DataList
where a DataObject inherits another DataObject.
If you for example want to restrict the number of pages that only have a
related Staff object:
$list = DataList::create('Page')
->InnerJoin('Staff', '"Staff"."ID" = "Page"."StaffID");
This will create a SQL query where the INNER JOIN is before the
LEFT JOIN of Page and SiteTree in the resulting SQL string. In MySQL
and PostgreSQL this will create an invalid query.
This patch solves the problem by sorting the joins.
efa9ff9b08