"If ONLY_FULL_GROUP_BY is disabled, a MySQL extension to the standard SQL use of GROUP BY permits the select list, HAVING condition, or ORDER BY list to refer to nonaggregated columns even if the columns are not functionally dependent on GROUP BY columns. This causes MySQL to accept the preceding query. In this case, the server is free to choose any value from each group, so unless they are the same, the values chosen are indeterminate, which is probably not what you want. Furthermore, the selection of values from each group cannot be influenced by adding an ORDER BY clause. "
ааааааааааааа ‎· мочь писать по-русски
а потом у меня разработчики спрашивают, как у нас внезапно работает "select x.* from xtable x group by x.id" ‎· мочь писать по-русски