Query failed: <pre>SELECT 
                    ep_sticky.value AS orderkey,

                    e.id,
                    e.title,
                    e.timestamp,
                    e.comments,
                    e.exflag,
                    e.authorid,
                    e.trackbacks,
                    e.isdraft,
                    e.allow_comments,
                    e.last_modified,

                    a.realname AS author,
                    a.username AS loginname,
                    a.email
                     , e.body, e.extended
                     
                FROM
                    serendipity_entries AS e
                    LEFT JOIN serendipity_authors a
                        ON e.authorid = a.authorid
                    LEFT JOIN serendipity_entrycat ec
                        ON e.id = ec.entryid
                    LEFT JOIN serendipity_category c
                        ON ec.categoryid = c.categoryid
                    INNER JOIN serendipity_entrytags AS entrytags ON (e.id = entrytags.entryid)  LEFT OUTER JOIN serendipity_entryproperties ep_access
                                              ON (e.id = ep_access.entryid AND ep_access.property = 'ep_access')
 LEFT JOIN serendipity_entryproperties ep_sticky
                                            ON (e.id = ep_sticky.entryid AND ep_sticky.property = 'ep_is_sticky') LEFT JOIN serendipity_authorgroups AS acl_a
                                   ON acl_a.authorid = 0
                            LEFT JOIN serendipity_access AS acl_acc
                                   ON (    acl_acc.artifact_mode = 'read'
                                       AND acl_acc.artifact_type = 'category'
                                       AND acl_acc.artifact_id   = c.categoryid
                                      )
                    WHERE isdraft = 'false' AND e.timestamp &lt;= 1606433400 AND entrytags.tag =  'education'   AND  (ep_access.property IS NULL OR ep_access.value = 'public')  AND     (
                                 c.categoryid IS NULL
                                 OR ( acl_acc.groupid = 0)
                                 OR ( acl_acc.artifact_id IS NULL
                                      
                                    )
                               )
                     GROUP BY e.id
                     
                     ORDER BY orderkey DESC, timestamp DESC
                      LIMIT 15</pre> / 'blogknow_s9.ep_sticky.value' isn't in GROUP BY