How do I query only rows where multiple instances with the same ID exist with Postgres?

I have a table where I want to gather some statistics, but only for items that are repeated two or more times. Here is how the a simplified table looks like: CREATE TABLE test ( id bigint, something text ); Most rows have a unique id, some have repeated entries where something differs. What I'm wondering is whether there is a way to read the table but only items that have 2 or more rows with the same id. I know how to count the number of duplicated rows using the COUNT() and GROUP BY: SELECT id, COUNT(id) AS count FROM test GROUP BY id; I don't really see how to use the COUNT(id) in a WHERE or FILTER clause (since aggregate functions are not allowed there). --- Just in case, a very small data sample would be: id | something ----|----------- 1 | first 2 | second 2 | third In the result I want to see: id | something ----|----------- 2 | second 2 | third