mysql的分组查询、分组统计

查询主题下的二级回复和三级回复列表spa SELECTimport a.topic_id,count(*) num FROM diz_reply AS a where a.parent_id<>'0' GROUP BY a.topic_idim 查询一个班的男生数和女生数：查询 SELECT grade, COUNT (CASE WHEN sex = 1 THEN 1 /*sex 1

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