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????1???????TEXT????BLOB?У?
????2??GROUP BY ???? DISTINCT ????а??????????512?????У?
????3?????UNION????UNION ALL???SELECT????а???????512?????У?
????????????????
????tmp_table_size???????????????????????С??
????http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_tmp_table_size
????max_heap_table_size: ???????????????????С??
????http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_max_heap_table_size
???????????????????????????С??????????????????С???
?????????????
?????????????????ζ???????????????????????????????????????????????????????t???????????????á? ???????????????????У?
????1??????????????ORDER BY????GROUP BY???????????????
????2??????????У????????￡?TEXT??BLOB??????512????????????????????????????????????????????????? ?????????????y???Щ?ж??????????????
????SQL???
?????????????????????????????????????????????SQL????????????????С????????SQL???Ч???
?????????????SQL????????￡?
????1?????SQL???
?????????????????????????飬????????????????????????????????????????????????????????????????????SQL???????????????????????С???????????????Ч?????????????????????????
????2??????????????????????
?????????????????????????????飬??????????????????????????????????????????????????????????????????????????????????????ж?????
????????ж????????????
???????explain????м????Extra?п???Using temporary??ζ?????????????