Syntax:
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 [mysql-indexes]. The DISTINCT keyword can be used to
find the minimum or maximum of the distinct values of expr, however,
this produces the same result as omitting DISTINCT.

MIN() and MAX() return NULL if there were no matching rows.
