Question

I’ve only dealt with one-to-one relationships in php so far, but I’m stuck on a problem which involves a one-to-many relationship. I’ve been sitting on this for a few days with no luck, so I’m desperate for someone to step in and show me a solution before I lose my mind.

In my database have a series of urls, which are received by a SELECT query along with various other fields, from different tables. Every url has at least one category associated with it, but can have multiple categories. So in my results I might see something that looks a bit like this:

link_id = 3   url= 'http://www.somesite1.com'   category = 'uncategorised' link_id = 4   url= 'http://www.somesite2.com'   category = 'travel' link_id = 4   url= 'http://www.somesite2.com'   category = 'fun' link_id = 4   url= 'http://www.somesite2.com'   category = 'misc' link_id = 3   url= 'http://www.somesite3.com'   category = 'uncategorised' 

I have got this to work, kind of. When I loop through and print them off, using a while loop and mysql fetch array, the result looks exactly like it does above. Thats great, except what I need is for it to read something like:

link_id = 4   url = 'http://www.somesite2.com'   category = 'travel fun misc' 

So that basically all of the categories for each url get combined somehow, as they are printed out. My first attempt led me to try a nested while loop, but it didn’t work and i’m not sure if this is feasible. Apart from that I’m wondering if I might need a multidimensional array (complete guess, i’ve never had to use one before).

I’m ordering these results by link id as above, so I know if the link id in the current loop iteration, matches the one in the last iteration – then I have something which has more than one category.. I think I’m really close, but I just can’t figure it out.

Any ideas?

Answer 1

There is also the ‘GROUP_CONCAT’ function in mysql. That should do exactly what you want to achieve.

Something like :

SELECT url, GROUP_CONCAT(category) AS categories FROM yourtable GROUP BY url