hether or not <TT
CLASS="LITERAL"
>users</TT
> has columns of those names.  Notice
    that we had to qualify the reference to <TT
CLASS="LITERAL"
>users.id</TT
> in the
    <TT
CLASS="LITERAL"
>WHERE</TT
> clause to make it refer to the table column.
    But we did not have to qualify the reference to <TT
CLASS="LITERAL"
>comment</TT
>
    as a target in the <TT
CLASS="LITERAL"
>UPDATE</TT
> list, because syntactically
    that must be a column of <TT
CLASS="LITERAL"
>users</TT
>.  We could write the same
