Question

So I have a table like this:

  Item Number     Collection       Items in Collection 
    1234         Madison Park                       
    2345         Madison Park                       
    3456         Madison Park                       
    6747         Belcaro                            
    5678         Belcaro                            

What I need is this:

  Item Number     Collection       Items in Collection 
    1234         Madison Park        1234, 2345, 3456     
    2345         Madison Park        1234, 2345, 3456     
    3456         Madison Park        1234, 2345, 3456     
    6747         Belcaro             6747, 5678           
    5678         Belcaro             6747, 5678           

Or better yet, this:

  Item Number     Collection       Items in Collection 
    1234         Madison Park        2345, 3456           
    2345         Madison Park        1234, 3456           
    3456         Madison Park        1234, 2345           
    6747         Belcaro             5678                 
    5678         Belcaro             6747                 

This isn’t my preferred method of getting the result, but due to client specifications the table needs to be set up this way. Also, it needs to be done through a MySQL Workbench Query. I’ve tried every variation of CONCAT_WS and GROUP_CONCAT I can think of but haven’t managed to come up with a solution. Group_Concat returns the results I want, but then it groups the collections, which won’t work. Ideas?

Answer 1

Try joining the table to itself on the grouped collection value. GROUP_CONCAT() will return a string, so you can REPLACE() the current rows’ item_number on it, however you don’t know exactly where the comma will be, so although it is a hack you can use SEPARATOR ' ' and then REPLACE() the item_number from the current row, replace occurrences of two spaces with one (the item_number was in the middle), TRIM() it (the item_number was on the end) and then replace the single spaces with a comma followed by a space:

SELECT i.item_number,
        i.collection,
        REPLACE(REPLACE(TRIM(REPLACE(g.items, i.item_number, '')), '  ', ' '), ' ', ', ') AS collection_items
FROM    item_table i
        INNER JOIN 
        (
            SELECT collection,
                    GROUP_CONCAT(item_number SEPARATOR ' ') AS items
            FROM item_table
            GROUP BY collection
        ) g ON g.collection = i.collection

I tested this locally and got your expected results.

SQLFiddle Demo