Question

I’m not sure what this is called but it happens all the time that you get a resultset like:

(id,name,age,favorite)
0,John Smith,21,Pepperoni 
1,John Smith,21,Ham
2,John Smith,21,Olives
3,John Doe,54,Tomatoes
4,John Doe,54,Potatoes 

Now when you’re iterating over this resultset, how can you concat the last column on rows that have similar name and ages? To get a result like John Smith,21,"Pepperoni,Ham,Olives". And what is this action called in general? I’m using JDBC-MySQL if that matters.

Thanks

Answer 1

This action could be done with GROUP_CONCAT in MySQL :

http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

SELECT name, age, GROUP_CONCAT(favorite SEPARATOR ',')
FROM myTable
GROUP BY name, age

Be careful, GROUP_CONCAT is only in MySQL and not a standard SQL.

You could not do that in other DBMS with a query.