This. I was appalled when I realized that MySQL will quietly seem to execute select x from y group by z x isn't a grouping column or an aggregate function,

This. I was appalled when I realized that MySQL will quietly seem to execute select x from y group by z x isn't a grouping column or an aggregate function, so where does it get the value for each group? It just arbitrarily picks a value from one of the rows, even if the other rows had different values!