get duplicated value in records

i have some 开发者_如何学Pythonrecords in a table. some of them have duplicated value in a field. i want to extract these duplicated values with mysql commands. how can i do that?

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You mean something like: I have a Person table, and there are multiple person with the same name, I want to find them?

You can do that using a group by clause:

select p.name, count(p.name) c 
from person p 
group by p.name 
having count(p.name) > 1

If you want to check duplicate multiple columns, then add all of them to the select and group by

select p.name, p.age, p.sex, count(*) c 
from person p 
group by p.name, p.age, p.sex 
having count(*) > 1