Question

I have two tables

Table one is a list of documents

documents:

+-------------+---------------+
| document_ID | document_name |
+-------------+---------------+
|    1        |   test.pdf    |
+-------------+---------------+
|    2        |  other.pdf    |
+-------------+---------------+

Table two is a list of users who have used that document. It is a 1-1 relationship – i.e. a user will only ever use a document ONCE (or not at all).

documents_users:

+-------------+---------------+-----------+---------------+
| document_ID | user_ID       | has_read  | (other stuff) |
+-------------+---------------+-----------+---------------+
|    1        |   5           |     1     |      stuff    |
+-------------+---------------+-----------+---------------+
|    1        |   7           |     1     |      stuff    |
+-------------+---------------+-----------+---------------+
|    2        |   5           |     1     |      stuff    |
+-------------+---------------+-----------+---------------+

When a user is browsing the list – I need to be able to show ALL documents, plus IF they have access it or not

So for example the desired output for user 5 in the example above is;

+-------------+---------------+-----------+---------------+
| document_ID | document_name |  has_read | (other stuff) |
+-------------+---------------+-----------+---------------+
|    1        |   test.pdf    |     1     |      stuff    |
+-------------+---------------+-----------+---------------+
|    2        |  other.pdf    |     1     |      stuff    |
+-------------+---------------+-----------+---------------+

while the desired output for user 7 is

+-------------+---------------+-----------+---------------+
| document_ID | document_name |  has_read | (other stuff) |
+-------------+---------------+-----------+---------------+
|    1        |   test.pdf    |     1     |   stuff       |
+-------------+---------------+-----------+---------------+
|    2        |  other.pdf    |           |               |
+-------------+---------------+-----------+---------------+

I tried doing a join along the lines of

$this->db->join('documents_users', 'documents_users.document_ID = documents.document_ID');
$this->db->where('documents_users.user_ID', '7');
return $this->get_all();

But this only returns the records that they has_read=1

I can see the problem is the “where” command – but I’m not sure what to do?

Answer 1

You need a (left) outer join, with the filter criterion on user_ID moved into the join condition rather than being in a WHERE clause:

$this->db->join(
   'documents_users',
   'documents_users.document_ID = documents.document_ID
AND documents_users.user_ID = 7',
   'left'
);