PHP Error

Love the functionality of this plug-in, but I’m getting the following PHP error in my logs:

[20-Feb-2013 01:42:38 UTC] WordPress database error Mixing of GROUP columns (MIN(),MAX(),COUNT(),…) with no GROUP columns is illegal if there is no GROUP BY clause for query
SELECT engine, SUM(data_length + index_length) AS size, table_rows
FROM information_schema.TABLES
WHERE table_schema = [DB NAME REMOVED]
AND table_name = ‘wp_comments’

I get this error for every table in my database.

http://ww.wp.xz.cn/extend/plugins/rvg-optimize-database/