先查询某字段重复的全部数据
select count(param) as count from table group by param having count > 1
(多个字段判断重复数据)
select count(param) as count1, count(param2) count2 from table group by param, param2 having count > 1 and count2 > 1
因为删除重复数据时肯定会保留一条，所以使用not in(not exists) 在重复数据中保留一条数据
select min(id) as id ,count(param) as count from table group by param having count > 1 //根据最大或最小值来进行数据保留
select count(param) as count from table where id not in (
select t.id from ( select min(id) as id ,count(param) as count from table group by param having count > 1 ) t
) group by param having count > 1
查询的sql已经写好，接下来就直接做删除操作
delete from table where id in 上面的sql
每次删除一个重复id，记得多执行几次