~ubuntu-branches/ubuntu/trusty/postgresql-9.3/trusty-updates : contents of doc/src/sgml/html/sql-fetch.html at revision 27

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><H1
><A
NAME="SQL-FETCH"
></A
>FETCH</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN78082"
></A
><H2
>Name</H2
>FETCH&nbsp;--&nbsp;retrieve rows from a query using a cursor</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN78090"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>FETCH [ <TT
CLASS="REPLACEABLE"
><I
>direction</I
></TT
> [ FROM | IN ] ] <TT
CLASS="REPLACEABLE"
><I
>cursor_name</I
></TT
>

<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>where <TT
CLASS="REPLACEABLE"
><I
>direction</I
></TT
> can be empty or one of:</SPAN
></SPAN
>

    NEXT
    PRIOR
    FIRST
    LAST
    ABSOLUTE <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>
    RELATIVE <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>
    <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>
    ALL
    FORWARD
    FORWARD <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>
    FORWARD ALL
    BACKWARD
    BACKWARD <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>
    BACKWARD ALL</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78101"
></A
><H2
>Description</H2
><P
>   <TT
CLASS="COMMAND"
>FETCH</TT
> retrieves rows using a previously-created cursor.
  </P
><P
>   A cursor has an associated position, which is used by
   <TT
CLASS="COMMAND"
>FETCH</TT
>.  The cursor position can be before the first row of the
   query result, on any particular row of the result, or after the last row
   of the result.  When created, a cursor is positioned before the first row.
   After fetching some rows, the cursor is positioned on the row most recently
   retrieved.  If <TT
CLASS="COMMAND"
>FETCH</TT
> runs off the end of the available rows
   then the cursor is left positioned after the last row, or before the first
   row if fetching backward.  <TT
CLASS="COMMAND"
>FETCH ALL</TT
> or <TT
CLASS="COMMAND"
>FETCH BACKWARD
   ALL</TT
> will always leave the cursor positioned after the last row or before
   the first row.
  </P
><P
>   The forms <TT
CLASS="LITERAL"
>NEXT</TT
>, <TT
CLASS="LITERAL"
>PRIOR</TT
>, <TT
CLASS="LITERAL"
>FIRST</TT
>,
   <TT
CLASS="LITERAL"
>LAST</TT
>, <TT
CLASS="LITERAL"
>ABSOLUTE</TT
>, <TT
CLASS="LITERAL"
>RELATIVE</TT
> fetch
   a single row after moving the cursor appropriately.  If there is no
   such row, an empty result is returned, and the cursor is left
   positioned before the first row or after the last row as
   appropriate.
  </P
><P
>   The forms using <TT
CLASS="LITERAL"
>FORWARD</TT
> and <TT
CLASS="LITERAL"
>BACKWARD</TT
>
   retrieve the indicated number of rows moving in the forward or
   backward direction, leaving the cursor positioned on the
   last-returned row (or after/before all rows, if the <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> exceeds the number of rows
   available).
  </P
><P
>   <TT
CLASS="LITERAL"
>RELATIVE 0</TT
>, <TT
CLASS="LITERAL"
>FORWARD 0</TT
>, and
   <TT
CLASS="LITERAL"
>BACKWARD 0</TT
> all request fetching the current row without
   moving the cursor, that is, re-fetching the most recently fetched
   row.  This will succeed unless the cursor is positioned before the
   first row or after the last row; in which case, no row is returned.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    This page describes usage of cursors at the SQL command level.
    If you are trying to use cursors inside a <SPAN
CLASS="APPLICATION"
>PL/pgSQL</SPAN
>
    function, the rules are different &mdash;
    see <A
HREF="plpgsql-cursors.html"
>Section 40.7</A
>.
   </P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78129"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>direction</I
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>direction</I
></TT
> defines
      the fetch direction and number of rows to fetch.  It can be one
      of the following:

      <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>NEXT</TT
></DT
><DD
><P
>          Fetch the next row. This is the default if <TT
CLASS="REPLACEABLE"
><I
>direction</I
></TT
> is omitted.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>PRIOR</TT
></DT
><DD
><P
>          Fetch the prior row.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>FIRST</TT
></DT
><DD
><P
>          Fetch the first row of the query (same as <TT
CLASS="LITERAL"
>ABSOLUTE 1</TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>LAST</TT
></DT
><DD
><P
>          Fetch the last row of the query (same as <TT
CLASS="LITERAL"
>ABSOLUTE -1</TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>ABSOLUTE <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
></DT
><DD
><P
>          Fetch the <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>'th row of the query,
          or the <TT
CLASS="LITERAL"
>abs(<TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>)</TT
>'th row from
          the end if <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is negative.  Position
          before first row or after last row if <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is out of range; in
          particular, <TT
CLASS="LITERAL"
>ABSOLUTE 0</TT
> positions before
          the first row.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>RELATIVE <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
></DT
><DD
><P
>          Fetch the <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>'th succeeding row, or
          the <TT
CLASS="LITERAL"
>abs(<TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
>)</TT
>'th prior
          row if <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is
          negative.  <TT
CLASS="LITERAL"
>RELATIVE 0</TT
> re-fetches the
          current row, if any.
         </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></DT
><DD
><P
>          Fetch the next <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> rows (same as
          <TT
CLASS="LITERAL"
>FORWARD <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>ALL</TT
></DT
><DD
><P
>          Fetch all remaining rows (same as <TT
CLASS="LITERAL"
>FORWARD ALL</TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>FORWARD</TT
></DT
><DD
><P
>          Fetch the next row (same as <TT
CLASS="LITERAL"
>NEXT</TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>FORWARD <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
></DT
><DD
><P
>          Fetch the next <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> rows.
          <TT
CLASS="LITERAL"
>FORWARD 0</TT
> re-fetches the current row.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>FORWARD ALL</TT
></DT
><DD
><P
>          Fetch all remaining rows.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>BACKWARD</TT
></DT
><DD
><P
>          Fetch the prior row (same as <TT
CLASS="LITERAL"
>PRIOR</TT
>).
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>BACKWARD <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
></DT
><DD
><P
>          Fetch the prior <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> rows (scanning
          backwards).  <TT
CLASS="LITERAL"
>BACKWARD 0</TT
> re-fetches the
          current row.
         </P
></DD
><DT
><TT
CLASS="LITERAL"
>BACKWARD ALL</TT
></DT
><DD
><P
>          Fetch all prior rows (scanning backwards).
         </P
></DD
></DL
></DIV
><P></P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is a
      possibly-signed integer constant, determining the location or
      number of rows to fetch.  For <TT
CLASS="LITERAL"
>FORWARD</TT
> and
      <TT
CLASS="LITERAL"
>BACKWARD</TT
> cases, specifying a negative <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is equivalent to changing
      the sense of <TT
CLASS="LITERAL"
>FORWARD</TT
> and <TT
CLASS="LITERAL"
>BACKWARD</TT
>.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>cursor_name</I
></TT
></DT
><DD
><P
>      An open cursor's name.
     </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78253"
></A
><H2
>Outputs</H2
><P
>   On successful completion, a <TT
CLASS="COMMAND"
>FETCH</TT
> command returns a command
   tag of the form
</P><PRE
CLASS="SCREEN"
>FETCH <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></PRE
><P>
   The <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
> is the number
   of rows fetched (possibly zero).  Note that in
   <SPAN
CLASS="APPLICATION"
>psql</SPAN
>, the command tag will not actually be
   displayed, since <SPAN
CLASS="APPLICATION"
>psql</SPAN
> displays the fetched
   rows instead.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78262"
></A
><H2
>Notes</H2
><P
>   The cursor should be declared with the <TT
CLASS="LITERAL"
>SCROLL</TT
>
   option if one intends to use any variants of <TT
CLASS="COMMAND"
>FETCH</TT
>
   other than <TT
CLASS="COMMAND"
>FETCH NEXT</TT
> or <TT
CLASS="COMMAND"
>FETCH FORWARD</TT
> with
   a positive count.  For simple queries
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> will allow backwards fetch
   from cursors not declared with <TT
CLASS="LITERAL"
>SCROLL</TT
>, but this
   behavior is best not relied on. If the cursor is declared with
   <TT
CLASS="LITERAL"
>NO SCROLL</TT
>, no backward fetches are allowed.
  </P
><P
>   <TT
CLASS="LITERAL"
>ABSOLUTE</TT
> fetches are not any faster than
   navigating to the desired row with a relative move: the underlying
   implementation must traverse all the intermediate rows anyway.
   Negative absolute fetches are even worse: the query must be read to
   the end to find the last row, and then traversed backward from
   there.  However, rewinding to the start of the query (as with
   <TT
CLASS="LITERAL"
>FETCH ABSOLUTE 0</TT
>) is fast.
  </P
><P
>   <A
HREF="sql-declare.html"
>DECLARE</A
>
   is used to define a cursor.  Use
   <A
HREF="sql-move.html"
>MOVE</A
>
   to change cursor position without retrieving data.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78278"
></A
><H2
>Examples</H2
><P
>   The following example traverses a table using a cursor:

</P><PRE
CLASS="PROGRAMLISTING"
>BEGIN WORK;

-- Set up a cursor:
DECLARE liahona SCROLL CURSOR FOR SELECT * FROM films;

-- Fetch the first 5 rows in the cursor liahona:
FETCH FORWARD 5 FROM liahona;

 code  |          title          | did | date_prod  |   kind   |  len
-------+-------------------------+-----+------------+----------+-------
 BL101 | The Third Man           | 101 | 1949-12-23 | Drama    | 01:44
 BL102 | The African Queen       | 101 | 1951-08-11 | Romantic | 01:43
 JL201 | Une Femme est une Femme | 102 | 1961-03-12 | Romantic | 01:25
 P_301 | Vertigo                 | 103 | 1958-11-14 | Action   | 02:08
 P_302 | Becket                  | 103 | 1964-02-03 | Drama    | 02:28

-- Fetch the previous row:
FETCH PRIOR FROM liahona;

 code  |  title  | did | date_prod  |  kind  |  len
-------+---------+-----+------------+--------+-------
 P_301 | Vertigo | 103 | 1958-11-14 | Action | 02:08

-- Close the cursor and end the transaction:
CLOSE liahona;
COMMIT WORK;</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78282"
></A
><H2
>Compatibility</H2
><P
>   The SQL standard defines <TT
CLASS="COMMAND"
>FETCH</TT
> for use in
   embedded SQL only.  The variant of <TT
CLASS="COMMAND"
>FETCH</TT
>
   described here returns the data as if it were a
   <TT
CLASS="COMMAND"
>SELECT</TT
> result rather than placing it in host
   variables.  Other than this point, <TT
CLASS="COMMAND"
>FETCH</TT
> is
   fully upward-compatible with the SQL standard.
  </P
><P
>   The <TT
CLASS="COMMAND"
>FETCH</TT
> forms involving
   <TT
CLASS="LITERAL"
>FORWARD</TT
> and <TT
CLASS="LITERAL"
>BACKWARD</TT
>, as well
   as the forms <TT
CLASS="LITERAL"
>FETCH <TT
CLASS="REPLACEABLE"
><I
>count</I
></TT
></TT
> and <TT
CLASS="LITERAL"
>FETCH
   ALL</TT
>, in which <TT
CLASS="LITERAL"
>FORWARD</TT
> is implicit, are
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extensions.
  </P
><P
>   The SQL standard allows only <TT
CLASS="LITERAL"
>FROM</TT
> preceding the cursor
   name; the option to use <TT
CLASS="LITERAL"
>IN</TT
>, or to leave them out altogether, is
   an extension.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN78301"
></A
><H2
>See Also</H2
><A
HREF="sql-close.html"
>CLOSE</A
>, <A
HREF="sql-declare.html"
>DECLARE</A
>, <A
HREF="sql-move.html"
>MOVE</A
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