Get list of duplicate rows in MySql

i have a table like this

ID     开发者_运维百科nachname     vorname
1       john         doe
2       john         doe
3       jim          doe
4       Michael     Knight

I need a query that will return all the fields (select *) from the records that have the same nachname and vorname (in this case, records 1 and 2). Can anyone help me with this? Thanks

The following query will give the list of duplicates :

SELECT n1.* FROM table n1
inner join table n2 on n2.vorname=n1.vorname and n2.nachname=n1.nachname
where n1.id <> n2.id

BTW The data you posted seems to be wrong "Doe" and "Knight" are a lastname, not a firstname :p.

The general solution to your problem is a query of the form

SELECT col1, col2, count(*)
FROM t1
GROUP BY col1, col2
HAVING count(*) > 1

This will return one row for each set of duplicate row in the table. The last column in this result is the number of duplicates for the particular values.

If you really want the ID, try something like this:

SELECT id FROM 
t1, 
( SELECT col1, col2, count(*)
  FROM t1
  GROUP BY col1, col2
  HAVING count(*) > 1 ) as t2
WHERE t1.col1 = t2.col1 AND t1.col2 = t2.col2 

Haven't tested it though

You can do it with a self-join:

select distinct t1.id from t as t1 inner join t as t2 
on t1.col1=t2.col1 and t1.col2=t2.col2 and t1.id<>t2.id

the t1.id<>t2.id is necessary to avoid ids matching against themselves. (If you want only 1 row out of each set of duplicates, you can use t1.id<t2.id).

select * from table AS t1 inner join
(select max(id) As id,nachname,vorname, count(*) 
from t1 group by nachname,vorname 
having count(*) >1) AS t2 on t1.id=t2.id

This should return ALL of the columns from the table where there is duplicate nachname and vorname. I recommend changing * to the exact columns that you need.

Edit: I added a max(id) so that the group by wouldn't be a problem. My query isn't as elegant as I would want though. There's probably an easier way to do it.