PostgreSQL在ID为ID的列中找到重复项

Question

For instance, I have a table say "Name" with duplicate records in it:

Id    |  Firstname
--------------------
1     |  John
2     |  John
3     |  Marc
4     |  Jammie
5     |  John
6     |  Marc

How can I fetch duplicate records and display them with their receptive primary key ID?

Answer 1

Use Count()Over() window aggregate function

Select * from
(
select Id, Firstname, count(1)over(partition by Firstname) as Cnt
from yourtable
)a
Where Cnt > 1

Answer 2

SELECT t.*
FROM t
INNER JOIN
(SELECT firstname
 FROM t
 GROUP BY firstname
 HAVING COUNT(*) > 1) sub
ON t.firstname = sub.firstname

A sub-query would do the trick. Select the first names that are found more than once your table, t. Then join these names back to the main table to pull in the primary key.