  the <SPAN
CLASS="QUOTE"
>"first row"</SPAN
> of a set is unpredictable unless the
    query is sorted on enough columns to guarantee a unique ordering
    of the rows arriving at the <TT
CLASS="LITERAL"
>DISTINCT</TT
> filter.
    (<TT
CLASS="LITERAL"
>DISTINCT ON</TT
> processing occurs after <TT
CLASS="LITERAL"
>ORDER
    BY</TT
> sorting.)
   </P
><P
>    The <TT
CLASS="LITERAL"
>DISTINCT ON</TT
> clause is not part of the SQL standard
    and is sometimes considered bad style because of the potentiall