Question

I have a table in mysql, let’s call it foo and it has a limitied amount of columns.

| id | name |    date    |
--------------------------
| 1  | bar  | 2012-05-08 |
| 2  | buba | 2012-05-09 |

My users can add records to the table foo_field (stuff like, code, description, time…).

| id | name        |
--------------------
| 1  | code        |
| 2  | description |
| 3  | time        |

In the table foo_field_value the values for the user-defined fields are stored, like so:

| id | foo_id | foo_field_id | value     |
------------------------------------------
| 1  | 1      | 1            | b         |
| 2  | 1      | 2            | Lalalala  |
| 3  | 1      | 3            | 12:00     |
| 1  | 2      | 1            | c         |
| 2  | 2      | 2            | We are go |
| 3  | 2      | 3            | 14:00     |

Ideally, I’d want one query which would give me a result like

| id | name | date       | code | description | time  |
------------------------------------------------------
| 1  | bar  | 2012-05-08 | b    | Lalalala    | 12:00 |
| 2  | buba | 2012-05-09 | c    | We are go   | 14:00 |

Is this even possible without doing an inner join on the foo_fields_value table for every foo_field (generating the query with PHP by doing another query first).

Answer 1

It’s possible to do it in just one, and quite simple.

We are going to modify the foo_field table a bit, adding a column corresponding to the foo table’s id column, which I assume is the primary key.

so now we have

* foo
|------|
| id   |
| name |
| date |
|------|

* foo_field
|-------------|
| foo_id      |
| code        |
| description |
| time        |
|-------------|

Which means we can add the extra fields with one simple query:

SELECT * FROM foo
LEFT JOIN foo_field ON foo.id = foo_field.foo_id

Which will give us a result set of

| id | name  |       date | foo_id | code   | description |     time |
|----+-------+------------+--------+--------+-------------+----------|
|  1 | asdw  | 2012-05-16 |      1 | asdasd | asdasd      | 15:03:41 |
|  2 | fdgfe | 2012-05-18 |      2 | asdas  | asdas       | 15:03:41 |
|  3 | asdw  | 2012-05-16 |      3 | asdas  | asdas       | 15:03:52 |
|  4 | fdgfe | 2012-05-18 |      4 | asdasd | asdasd      | 15:03:52 |

I am still not sure I surely understood your question. If you want to create truly dynamic values and datastructures, I suggest you save a serialized array into a TEXT field in your database, but I also suggest you to overlook your solution if this is the case; if you want your solution to be able to grow, you want to manage as strict structures as possible.