Mark, and any other interested reader: The group_concat() function is documented, for N effective calls, to concatenate N argument 1 values separated by N-1 argument 2 (or its default) values. It is completely undocumented which one of the passed-in argument 2 values is dropped. In the interest of code simplicity and performance, I am about to cause the Nth argument 2 value to be dropped instead of the 1st argument 2 value as happens with existing releases. I would be interested to see the best argument for retaining the current undocumented behavior, in particular some affected, reasonable use case(s). (No need to bother saying undocumented behavior should never change. We see that as having value which competes with other values.)