数据库查重

查重语句 select * from team where teamId in (select teamId from team group by teamId having count(teamId)> 1) select * from team where ID = 2 group by ID having count(*)>1 删除重复记录 delete from team where teamName in (select teamName from team group by teamName having count(teamName) > 1) and teamId not in (select min(teamId) from team group by teamName having count(teamName)>1)   查找表中多余的重复记录（多个字段） select * from team t where (t.teamId,t.teamOrg) in (select teamId,teamOrg from team group by teamId,teamOrg having count(*) > 1)   对单个数据去重 select distinct name from members; --这意味着从members表中取出去重后的name值   对多个字段进行去重时 select distinct name,age from members; --这意味着从members表中过滤掉name + age相同的值 --同样意味着，distinct这个关键字不能在同时查询两个及以上字段的时候，只过滤一个字段，而考虑其他的字段   distinct与count()函数相结合的方法 select count(distinct name) from members; --这意味着从members表中查询过滤后的name的总数 select age,count(distinct name) from members group by age;   distinct用在所有字段之前 select distinct name,age from members; --这种情况是对的 select  name,distinct age from members; --这种MySQL中会报语法错误   如果想对两个字段中的一个去重，而另外一个不去重的替代方法 select name,age from members where name in (select distinct name from members); --这种子查询可以对两个字段中的一个去重，而另外一个不去重，效率较低   Group by -- 列出 task_id 的所有唯一值（去重后的记录,null也是值） select task_id from Task group by task_id;   -- 任务总数 select count(task_id) task_numfrom (select task_id from Task group by task_id) tmp;