mysql的分組查詢、分組統計

查詢主題下的二級回覆和三級回覆列表spa SELECTimport a.topic_id,count(*) num FROM diz_reply AS a where a.parent_id<>'0' GROUP BY a.topic_idim 查詢一個班的男生數和女生數：查詢 SELECT grade, COUNT (CASE WHEN sex = 1 THEN 1 /*sex 1

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