>UPDATE</TT
> (and also in
    <TT
CLASS="COMMAND"
>DELETE</TT
>) statements: the current tuple ID
    (<ACRONYM
CLASS="ACRONYM"
>CTID</ACRONYM
>).
    This is a system column containing the
    file block number and position in the block for the row. Knowing
    the table, the <ACRONYM
CLASS="ACRONYM"
>CTID</ACRONYM
> can be used to retrieve the
    original row of <TT
CLASS="LITERAL"
>t1</TT
> to be updated.  After adding the
    <ACRONYM
CLASS="ACRONYM"
>CTID</ACRONYM
> to the target list, the query actu