   MIN([DISTINCT] expr)
   MAX([DISTINCT] expr)
Returns the minimum or maximum value of expr.  MIN() and
MAX() may take a string argument; in such cases they return the
minimum or maximum string value. See also : [MySQL indexes].
The DISTINCT keyword can be used as of MySQL 5.0.0 to find the minimum
or maximum of the distinct values of expr; this is supported, but
produces the same result as omitting DISTINCT.
