SQL Count Rows From Multiple tables

Question

Lets say i have 2 tables

Companies

company_id    
name

Users

id
company_id
name

each company has multiple users assign to it... which is referenced in the company_id field from each record in the users table

HOW can i get a record showing the (company_id), (company_name) and (number or users)

for eg:

id# 1234 | name# Microsoft | n of users# 2000 

I dont know how to make this query, i know i have to use the function COUNT() but i dont know how

Answer 1

If you want to get all companies even if they don't have any users yet use OUTER JOIN

SELECT c.company_id, c.name company_name, COUNT(u.id) no_of_users
  FROM companies c LEFT JOIN users u
    ON c.company_id = u.company_id
 GROUP BY c.company_id, c.name

Sample output:

| COMPANY_ID | COMPANY_NAME | NO_OF_USERS |
|------------|--------------|-------------|
|          1 |     Company1 |           3 |
|          2 |     Company2 |           2 |
|          3 |     Company3 |           0 |

Here is SQLFiddle demo

Answer 2

Try :

SELECT companies.company_id,companies.company_name,COUNT(users.id)
FROM companies, users
WHERE companies.id = users.company_id
group by companies.id

Answer 3

这将是查询

select Companies.company_id,Companies.name,count(Users .id) from Companies,Users where Companies=company_id  and Users =company_id group by company_id