Hi,

While testing an upgrade from 1.9.19+20120712 to 2.2.*, I noticed that upgrading to 2.2.4+20120802 worked while upgrading from 2.2.4+20120809 failed with the following error:

> Default exception handler: Error reading from database Debug: ERROR: syntax error at or near "count"
> LINE 1: ...newestid, contextid, lowerboundary, letter, COUNT('x') count
> ^
> SELECT MAX(id) as newestid, contextid, lowerboundary, letter, COUNT('x') count
> FROM mdl_grade_letters
> GROUP BY contextid, lowerboundary, letter
> HAVING COUNT('x') > 1
> [array (
> )]

By git-blaming, I quickly found that this code was added to fix MDL-30515 but unfortunately, it makes the ugprade fail on its own.