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怎么去除mysql字段中的重复值

MySQL查询重复字段,及删除重复记录的方法 数据库中有个大表,需要查找其中的名字有重复的记录id,以便比较。如果仅仅是查找数据库中name不重复的字段,很容易: SELECT min(`id`),`name` FROM `table` GROUP BY `name`; 但是这样并不能得到说有重...

方法有很多,这里介绍两种 方法一、如果要保留id的最小值,例如: 数据:执行sql:select count(*) as count ,name,id from ceshi group by name<img 最后要删除的sql为:delete from ceshi where id not in (select count(*) as count ,n...

MySQL查询重复字段,及删除重复记录的方法 数据库中有个大表,需要查找其中的名字有重复的记录id,以便比较。如果仅仅是查找数据库中name不重复的字段,很容易: SELECT min(`id`),`name` FROM `table` GROUP BY `name`; 但是这样并不能得到说有重...

假设表名为test: select * from (select *, concat(name,code) as __f from test order by date desc) __t group by __f;

select name,grade,testGrade,count(*) from t_student group by (name,grade,testGrade) having count(*)>1 where grade is null

select * from table ###where not exists (select * from table ###where # = #and ## < ##) 在使用mysql时,有时需要查询出某个字段不重复的记录,虽然mysql提供 有distinct这个关键字来过滤掉多余的重复记录只保留一条,但往往只用它来返回不...

-- 保留相同A值的最小id行 select * from table_a a where not exists ( select 1 from table_a b where b.A = a.A and b.id < a.id )

1. 查询需要删除的记录,会保留一条记录。 select a.id,a.subject,a.RECEIVER from test1 a left join (select c.subject,c.RECEIVER ,max(c.id) as bid from test1 c where status=0 GROUP BY RECEIVER,SUBJECT having count(1) >1) b on a.id<...

:例: 表: tb 里面 有3个字段 id name type 值: 小明 34 小明 46 小明 ... 答:分组显示:SELECT * FROM tb GROUP BY name 去除重复数据可以使用DISTINCT SELECT DISTINCT * FROM tb GROUP BY name

SELECT * FROM names;+----+--------+| id | name |+----+--------+| 1 | google || 2 | yahoo || 3 | msn || 4 | google || 5 | google || 6 | yahoo | 想保留最大id的话: DELETE FROM NAMES WHERE id NOT IN (SELECT * FROM (SELECT MAX(n.id...

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