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<>超级SQL的开始
## 查询重复的数据 SELECT m.ma_code, count(1) FROM bi_matierals m GROUP BY m.ma_code
HAVING count(1) >1 ## 查看重复数据 id不等于 最大的那个 SELECT * FROM bi_matierals ta WHERE
ta.id<>( SELECT t.maxid FROM (SELECT max(id) as maxid from bi_matierals as tb
where ta.ma_code= tb.ma_code) t )
<>重要结论
select方法 返回的是一个 table， 所以取了别名，才可以拿来用，才可以from t
<>应用实例1
# 202种标准件 在 非标准件里面有 重复记录， 查出这些重复数据 SELECT a.id, a.ma_code, a.ma_name,
a.ma_specification, a.is_norm, a.`status` FROM bi_matierals AS a JOIN
bi_matierals AS b ON a.ma_specification=b.ma_specification WHERE a.is_norm = '0'
and b.is_norm= '1' # 逻辑删除上面 找出的数据（join查出来的是子表，我们只能更新主表） UPDATE bi_matierals c
join (SELECT a.id, a.ma_code, a.ma_name, a.ma_specification, a.is_norm, a.`
status` FROM bi_matierals AS a JOIN bi_matierals AS b ON a.ma_specification=
b.ma_specification WHERE a.is_norm= '0' and b.is_norm = '1') d ON c.id = d.id
set c.`Status` = 2