Is it possible to count all rows with the same id with COUNT?

Question

PostgreSQL 9.4.

I have the following table:

   id             player_id
serial PK          integer
---------------------------
   1              


        

Answer 1

If all you need is a count of the number of rows where player_id is 1, then you can do this:

SELECT count(*)
FROM your_table_name
WHERE player_id = 1;

If you want to count the number of rows for each player_id, then you will need to use a GROUP BY:

SELECT player_id, count(*)
FROM your_table_name
GROUP BY player_id;