将输入存储在mysql数组中

Question

I got a text field for entering the new categories and submit with ajax ..

My script is working but everytime i submit new category mysql is creating one row to hold single category name .

I would like to create something like this eachtime when i add a new category the same single row should get updated

Id.   User id.   Category
 1.      23.          Personal , shopping , others +

So everytime i update a category name the row should be updated with the comma separated value . And also i would like to fetch the result in a select box