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SELECT A.* ,B.type FROM Table_A A LEFT JOIN Table_B B ON A.id=B.id WHERE B.type=1改为SELECT A.* ,B.type FROM Table_A A LEFT JOIN Table_B B ON A.id=B.id AND B.type=1原因sql1是在SELECT A.* ,B.type FROM Ta...

select a.grade,a.course from (select count(*) s ,grade,course from t GROUP BY course,grade )aleft join (select max(s) s,course from (select count(*) s ,grade,course from t GROUP BY grade,course) t GROUP BY course) bon a.course=b.coursewhere a.s=b.s