Question

This is probably very simple, but for some reason I am pulling a blank on this one..

I want to join two tables and get the total occurrences of a column in one table within another table.
Table1

id | company
------------
 1 | companyA
 2 | companyB
 3 | companyC


Table2

id | company_id
------------
 1 |  2
 2 |  2
 3 |  1
 4 |  2
 5 |  3

The result should be:

company | count(*)
------------------
companyA| 1
companyB| 3
companyC| 1

I can’t seem to get the count portion correct. I was thinking that it would be something like:

SELECT Table1.company, count(*)
FROM Table1 JOIN Table2 ON
Table1.id = Table2.company_id
GROUP BY Table1.company;

Revised: The problem is actually that companyA and companyB come up correctly, but it’s not showing companyC. I went through and double checked that there are matches in the fields for companyC which there were.

Answer 1

it should be Table2.company_id that you are joining with and not Table2.id

SELECT  Table1.company, count(*)
FROM    Table1 
        INNER JOIN Table2 
           ON Table1.id = Table2.company_id  -- <<== here
GROUP   BY Table1.company;

you must define an INDEX (probably UNIQUE) on column company of table for faster performance since you are grouping it with company

UPDATE 1

SELECT  Table1.company, count(Table2.company_id)
FROM    Table1 
        LEFT JOIN Table2 
           ON Table1.id = Table2.company_id  -- <<== here
GROUP   BY Table1.company;

• SQLFiddle Demo