Current File : //opt/alt/postgresql11/usr/share/doc/alt-postgresql11-9.2.24/html/sql-fetch.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>FETCH</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 9.2.24 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="SQL Commands"
HREF="sql-commands.html"><LINK
REL="PREVIOUS"
TITLE="EXPLAIN"
HREF="sql-explain.html"><LINK
REL="NEXT"
TITLE="GRANT"
HREF="sql-grant.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2017-11-06T22:43:11"></HEAD
><BODY
CLASS="REFENTRY"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
><A
HREF="index.html"
>PostgreSQL 9.2.24 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="EXPLAIN"
HREF="sql-explain.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="sql-commands.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="GRANT"
HREF="sql-grant.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><H1
><A
NAME="SQL-FETCH"
></A
>FETCH</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN75525"
></A
><H2
>Name</H2
>FETCH -- retrieve rows from a query using a cursor</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN75533"
></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="AEN75544"
></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 —
see <A
HREF="plpgsql-cursors.html"
>Section 39.7</A
>.
</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN75572"
></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="AEN75696"
></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="AEN75705"
></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="AEN75721"
></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="AEN75725"
></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="AEN75744"
></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
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="sql-explain.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="sql-grant.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>EXPLAIN</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="sql-commands.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>GRANT</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
Mini Shell