wow, dig up an old thread, why dontcha...

say you have a vendors table, and a one-to-many relationship from vendors to their products

and suppose you wanted to retrieve vendors along with the product name, product size, product colour, and product price

you could do one GROUP_CONCAT for product name, another GROUP_CONCAT for product size, another GROUP_CONCAT for product colour, and yet another GROUP_CONCAT for product price

the result set might look like this --
vendor        GROUP_CONCAT(product_name)               GROUP_CONCAT(product_size)  GROUP_CONCAT(product_colour)  GROUP_CONCAT(product_price)
Widgets R Us  SuperWidget,RegularWidget,TeenieWidget   Large,Medium,Small          Plain,Plain,Plain             10.99,9.37,4.98
Acme Inc      Anvil,Rocket,Chainsaw                    Jumbo,OneSize,None          Black,Silver,None             25.00,149.99,50.00
see how messy that gets? you ~need~ a front-end application language to be able to discombobulate all the concatenated stuff and re-assemble the product rows

more than one or two columns like this is ungainly