ally looks like:

</P><PRE
CLASS="PROGRAMLISTING"
>SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;</PRE
><P>

    Now another detail of <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> enters
    the stage. Old table rows aren't overwritten, and this
    is why <TT
CLASS="COMMAND"
>ROLLBACK</TT
> is fast. In an <TT
CLASS="COMMAND"
>UPDATE</TT
>,
    the new result row is inserted into the table (after stripping the
    <ACRONYM
CLASS="ACRONYM"
>CTID</ACRONYM
>) and in the row header of the old row, w