multidimensional array

Hi list, In order to avoid many left joins I took an aproach that I didn't know if it's good, but I couldn't figure out another way. If my cliente has 10 phone numbers I buld an array, serialize it and store in database, so I didn't have to create another table. The problem is now I need to migrate the data to this format, how can I select the multiple data and put in multidimensional array at runtime to store again. for example I need to put all fileds with graduation and all fields with discipline with equal id in array named school serialize it and after insert in another table. Thank's Rodrigo