Keep_on_Growing的博客

SELECT `字段名a`, count(`字段名a`) as c FROM `表名` WHERE 过滤条件 group by 字段名a ORDER BY `c` DESC

查询NULL值：SELECT * FROM `表名` WHERE "字段名" IS NULL查询非空值：SELECT * FROM `表名` WHERE "字段名" IS NOT NULL删除空数据：DELETE FROM '表名' WHERE '字段名' IS NULL ...

 由于MySQL无法在同一张表上同时进行删除和查询操作：解决方案：建立一张临时表tmpresult：delete from partno_sup where id in (select id from (select id from partno_sup where partno in (select partno from partno_sup group by partno ...