MySQL-从另一个表中查询与当前表相同的ID的字段

Question

This is a quite complex project having specific reasons for the way it is setup, but for ease of learning purposes, I've replaced the subject with just names.

For example, I have two tables:

Servers (stores unique server names)

• server_id (unique id)
• server_name

Clients (stores all the clients in the company)

• server_id (matches the unique id from servers table)
• .. other columns

What I'm trying to do is list the distinct server names from the first table, along with the number of clients that use each server id. But instead of returning the server "id", I'd like to return the "name". Right now I have this:

SELECT DISTINCT server_id, count(server_name) AS count 
  FROM clients 
 GROUP BY server_id

This returns the server id instead of the name. How do I fix that? Complete beginner to SQL and mySQL by the way.

Answer 1

Try

SELECT s.server_id, 
       s.server_name, 
       COUNT(*) count_clients
  FROM clients c JOIN servers s 
    ON c.server_id = s.server_id
  GROUP BY s.server_id, s.server_name

Output:

| SERVER_ID | SERVER_NAME | COUNT_CLIENTS |
-------------------------------------------
|         1 |     server1 |             2 |
|         2 |     server2 |             4 |

SQLFiddle