Is that mySQL? I don't recall seeing the + being used as a string concatenator before. If it is mySQL GROUP_CONCAT might do what you want, but it has length limits associated with it. It'd probably be best to do it outside of mySQL. A lot of languages give the capability of joining (or splitting) an array.
The moon on the one hand, the dawn on the other:
The moon is my sister, the dawn is my brother.
The moon on my left and the dawn on my right.
My brother, good morning: my sister, good night.
-- Hilaire Belloc