Question

I have two tables in my database

table: products                   table: companies
+-----------+------------+        +------+------------+
| name      | company_id |        | id   | name       |
+-----------+------------+        +------+------------+
|Product 1  | 1          |        | 1    | Company 1  |
|Product 2  | 1          |        | 2    | Company 2  |   
|Product 3  | 3          |        | 3    | Company 3  |
|Product 4  | 1          |        | 4    | Company 4  |
|Product 5  | 1          |        | ...               |
|Product 6  | 3          |        +------+------------+
|Product 7  | 2          |
|...                     |
+-----------+------------+

Now I have to make company-selector (filtering products by company) using HTML SELECT element with names of all companies from table companies and COUNT of products after company name in the list.

So, my goal is to get SELECT options like this:

• Company 1 (4)
• Company 2 (1)
• Company 3 (2)
• Company 4 (0)

(note: counts inside the brackets are from example above)

What have I tried so far?

I was using mysql_* functions earlier and later it was mysqli procedural model. I can do this manually with one query for companies and another one inside while block to get COUNT of elements (filtered by current company’s id in the loop). Now I’m trying to work with PDO object which is something new for me and I’m not very familiar with it.

Question

Is it somehow possible to get COUNT with one query (using JOINs or something)? If not, how I can do it with query inside the loop (old way) using my $dbPDO object? Or any other way?

I’ve looked some examples here but nothing could adapt to fit my requirements. Maybe I missed something but working with PDO is still painful for me (and I must learn it ASAP).

Looking at my own question, I don’t think it’s something hard, but the worst thing, I can’t find solution by myself.

At the end, I have solution in mysqli, just I don’t like it so much and think there’s easier way of making this task done!

I thought this question is something I need but still don’t understand that query in answer.

So far I have this code and have no idea how to make it counts products:

  $dbPDO = new PDO('mysql:dbname=comixdb;host=localhost', 'root', '');
  $sel_cat = ''; # selector HTML
  $sql = "SELECT * FROM categories ORDER BY name";
  foreach ($dbPDO->query($sql) as $row) {
    $sel_cat .= "<option value=\"{$row['id']}\">{$row['name']}</option>";
    }
  $sel_cat = "<select><option value=\"*\">All categories</option>$sel_cat</select>";

  echo $sel_cat;

Hope I’ve clarified question enough. Any help would be appreciated.

Answer 1

What you need can be done in SQL:

SELECT companies.name, SUM(IF(company_id IS NULL, 0, 1)) AS products
    FROM companies
    LEFT JOIN products ON (companies.id = products.company_id)
    GROUP BY companies.id;

The LEFT JOIN ensures that all companies get selected, and the SUM ensures that the count is correct (a simple COUNT would return 1 for companies with no products).