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Last round of reference page editing.

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Peter Eisentraut
2003-05-04 02:23:16 +00:00
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doc/src/sgml/ref/fetch.sgml
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@@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/fetch.sgml,v 1.28 2003/03/27 16:51:27 momjian Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/fetch.sgml,v 1.29 2003/05/04 02:23:16 petere Exp $
PostgreSQL documentation
-->
@@ -8,19 +8,14 @@ PostgreSQL documentation
<refentrytitle id="SQL-FETCH-TITLE">FETCH</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
FETCH
</refname>
<refpurpose>
retrieve rows from a query using a cursor
</refpurpose>
<refname>FETCH</refname>
<refpurpose>retrieve rows from a query using a cursor</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>2003-03-11</date>
</refsynopsisdivinfo>
<synopsis>
<synopsis>
FETCH [ <replaceable class="PARAMETER">direction</replaceable> { FROM | IN } ] <replaceable class="PARAMETER">cursor</replaceable>
where <replaceable class="PARAMETER">direction</replaceable> can be empty or one of:
@@ -39,243 +34,20 @@ where <replaceable class="PARAMETER">direction</replaceable> can be empty or one
BACKWARD
BACKWARD <replaceable class="PARAMETER">count</replaceable>
BACKWARD ALL
</synopsis>
<refsect2 id="R2-SQL-FETCH-1">
<refsect2info>
<date>2003-03-11</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">direction</replaceable></term>
<listitem>
<para>
<replaceable class="PARAMETER">direction</replaceable>
defines the fetch direction and number of rows to fetch.
It can be one of the following:
<variablelist>
<varlistentry>
<term>NEXT</term>
<listitem>
<para>
fetch next row. This is the default
if <replaceable class="PARAMETER">direction</replaceable> is omitted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PRIOR</term>
<listitem>
<para>
fetch prior row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FIRST</term>
<listitem>
<para>
fetch first row of query (same as ABSOLUTE 1).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LAST</term>
<listitem>
<para>
fetch last row of query (same as ABSOLUTE -1).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ABSOLUTE <replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
fetch the <replaceable class="PARAMETER">count</replaceable>'th
row of query, or the
abs(<replaceable class="PARAMETER">count</replaceable>)'th row
from the end if
<replaceable class="PARAMETER">count</replaceable> &lt; 0.
Position before first row or after last row
if <replaceable class="PARAMETER">count</replaceable> is out of
range; in particular, ABSOLUTE 0 positions before first row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>RELATIVE <replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
fetch the <replaceable class="PARAMETER">count</replaceable>'th
succeeding row, or the
abs(<replaceable class="PARAMETER">count</replaceable>)'th prior
row if <replaceable class="PARAMETER">count</replaceable> &lt; 0.
RELATIVE 0 re-fetches current row, if any.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
fetch the next <replaceable class="PARAMETER">count</replaceable>
rows (same as FORWARD <replaceable class="PARAMETER">count</replaceable>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>ALL</term>
<listitem>
<para>
fetch all remaining rows (same as FORWARD ALL).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FORWARD</term>
<listitem>
<para>
fetch next row (same as NEXT).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FORWARD <replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
fetch next <replaceable class="PARAMETER">count</replaceable>
rows. FORWARD 0 re-fetches current row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>FORWARD ALL</term>
<listitem>
<para>
fetch all remaining rows.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>BACKWARD</term>
<listitem>
<para>
fetch prior row (same as PRIOR).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>BACKWARD <replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
fetch prior <replaceable class="PARAMETER">count</replaceable>
rows (scanning backwards). BACKWARD 0 re-fetches current row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>BACKWARD ALL</term>
<listitem>
<para>
fetch all prior rows (scanning backwards).
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
<replaceable class="PARAMETER">count</replaceable>
is a possibly-signed integer constant, determining the location
or number of rows to fetch. For FORWARD and BACKWARD cases,
specifying a negative <replaceable
class="PARAMETER">count</replaceable>
is equivalent to changing the sense of FORWARD and BACKWARD.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">cursor</replaceable></term>
<listitem>
<para>
An open cursor's name.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-FETCH-2">
<refsect2info>
<date>2003-03-11</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<command>FETCH</command> returns rows from the result of the query defined
by the specified cursor.
The following messages will be returned if the query fails:
<variablelist>
<varlistentry>
<term><computeroutput>
WARNING: PerformPortalFetch: portal "<replaceable class="PARAMETER">cursor</replaceable>" not found
</computeroutput></term>
<listitem>
<para>
There is no cursor with the specified name.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</synopsis>
</refsynopsisdiv>
<refsect1 id="R1-SQL-FETCH-1">
<refsect1info>
<date>2003-03-11</date>
</refsect1info>
<title>
Description
</title>
<refsect1>
<title>Description</title>
<para>
<command>FETCH</command> retrieves rows using a cursor.
</para>
<para>
A cursor has an associated <firstterm>position</> that is used by
A cursor has an associated position, which is used by
<command>FETCH</>. The cursor position can be before the first row of the
query result, or on any particular row of the result, or after the last row
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 <command>FETCH</> runs off the end of the available rows
@@ -286,166 +58,338 @@ WARNING: PerformPortalFetch: portal "<replaceable class="PARAMETER">cursor</rep
</para>
<para>
The SQL-compatible forms (NEXT, PRIOR, FIRST, LAST, ABSOLUTE, RELATIVE)
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.
The forms <literal>NEXT</>, <literal>PRIOR</>, <literal>FIRST</>,
<literal>LAST</>, <literal>ABSOLUTE</>, <literal>RELATIVE</> 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.
</para>
<para>
The forms using FORWARD and BACKWARD are not in the SQL standard, but
are <productname>PostgreSQL</productname> extensions. These forms
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 <replaceable
The forms using <literal>FORWARD</> and <literal>BACKWARD</>
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 <replaceable
class="PARAMETER">count</replaceable> exceeds the number of rows
available).
</para>
<tip>
<para>
RELATIVE 0, FORWARD 0, and BACKWARD 0 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.
</para>
</tip>
<refsect2 id="R2-SQL-FETCH-3">
<refsect2info>
<date>2003-03-11</date>
</refsect2info>
<title>
Notes
</title>
<para>
The cursor should be declared with the SCROLL option if one intends to
use any variants of <command>FETCH</> other than <command>FETCH NEXT</>
or <command>FETCH FORWARD</> with a positive count. For simple queries
<productname>PostgreSQL</productname> will allow backwards fetch from
cursors not declared with SCROLL, but this behavior is best not
relied on. If the cursor is declared with NO SCROLL, no backward
fetches are allowed.
</para>
<para>
ABSOLUTE 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 FETCH ABSOLUTE 0) is fast.
</para>
<para>
Updating data via a cursor is not supported by
<productname>PostgreSQL</productname>, because mapping cursor
updates back to base tables is not generally possible, as is also
the case with view updates. Consequently, users must issue
explicit <command>UPDATE</command> commands to replace data.
</para>
<para>
<xref linkend="sql-declare" endterm="sql-declare-title">
is used to define a cursor.
Use
<xref linkend="sql-move" endterm="sql-move-title">
to change cursor position without retrieving data.
</para>
</refsect2>
<para>
<literal>RELATIVE 0</>, <literal>FORWARD 0</>, and
<literal>BACKWARD 0</> 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.
</para>
</refsect1>
<refsect1 id="R1-SQL-FETCH-2">
<title>
Usage
</title>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">direction</replaceable></term>
<listitem>
<para>
<replaceable class="PARAMETER">direction</replaceable> defines
the fetch direction and number of rows to fetch. It can be one
of the following:
<variablelist>
<varlistentry>
<term><literal>NEXT</literal></term>
<listitem>
<para>
Fetch the next row. This is the default if <replaceable
class="PARAMETER">direction</replaceable> is omitted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>PRIOR</literal></term>
<listitem>
<para>
Fetch the prior row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>FIRST</literal></term>
<listitem>
<para>
Fetch the first row of the query (same as <literal>ABSOLUTE 1</literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>LAST</literal></term>
<listitem>
<para>
Fetch the last row of the query (same as <literal>ABSOLUTE -1</literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ABSOLUTE <replaceable class="PARAMETER">count</replaceable></literal></term>
<listitem>
<para>
Fetch the <replaceable
class="PARAMETER">count</replaceable>'th row of the query,
or the <literal>abs(<replaceable
class="PARAMETER">count</replaceable>)</literal>'th row from
the end if <replaceable
class="PARAMETER">count</replaceable> is negative. Position
before first row or after last row if <replaceable
class="PARAMETER">count</replaceable> is out of range; in
particular, <literal>ABSOLUTE 0</literal> positions before
the first row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>RELATIVE <replaceable class="PARAMETER">count</replaceable></literal></term>
<listitem>
<para>
Fetch the <replaceable
class="PARAMETER">count</replaceable>'th succeeding row, or
the <literal>abs(<replaceable
class="PARAMETER">count</replaceable>)</literal>'th prior
row if <replaceable class="PARAMETER">count</replaceable> is
negative. <literal>RELATIVE 0</literal> re-fetches the
current row, if any.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
Fetch the next <replaceable
class="PARAMETER">count</replaceable> rows (same as
<literal>FORWARD <replaceable
class="PARAMETER">count</replaceable></literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ALL</literal></term>
<listitem>
<para>
Fetch all remaining rows (same as <literal>FORWARD ALL</literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>FORWARD</literal></term>
<listitem>
<para>
Fetch the next row (same as <literal>NEXT</literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>FORWARD <replaceable class="PARAMETER">count</replaceable></literal></term>
<listitem>
<para>
Fetch the next <replaceable
class="PARAMETER">count</replaceable> rows.
<literal>FORWARD 0</literal> re-fetches the current row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>FORWARD ALL</literal></term>
<listitem>
<para>
Fetch all remaining rows.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>BACKWARD</literal></term>
<listitem>
<para>
Fetch the prior row (same as <literal>PRIOR</literal>).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>BACKWARD <replaceable class="PARAMETER">count</replaceable></literal></term>
<listitem>
<para>
Fetch the prior <replaceable
class="PARAMETER">count</replaceable> rows (scanning
backwards). <literal>BACKWARD 0</literal> re-fetches the
current row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>BACKWARD ALL</literal></term>
<listitem>
<para>
Fetch all prior rows (scanning backwards).
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">count</replaceable></term>
<listitem>
<para>
<replaceable class="PARAMETER">count</replaceable> is a
possibly-signed integer constant, determining the location or
number of rows to fetch. For <literal>FORWARD</> and
<literal>BACKWARD</> cases, specifying a negative <replaceable
class="PARAMETER">count</replaceable> is equivalent to changing
the sense of <literal>FORWARD</> and <literal>BACKWARD</>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">cursor</replaceable></term>
<listitem>
<para>
An open cursor's name.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Diagnostics</title>
<variablelist>
<varlistentry>
<term><computeroutput>WARNING: PerformPortalFetch: portal "<replaceable class="PARAMETER">cursor</replaceable>" not found</computeroutput></term>
<listitem>
<para>
There is no cursor with the specified name.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
The cursor should be declared with the <literal>SCROLL</literal>
option if one intends to use any variants of <command>FETCH</>
other than <command>FETCH NEXT</> or <command>FETCH FORWARD</> with
a positive count. For simple queries
<productname>PostgreSQL</productname> will allow backwards fetch
from cursors not declared with <literal>SCROLL</literal>, but this
behavior is best not relied on. If the cursor is declared with
<literal>NO SCROLL</literal>, no backward fetches are allowed.
</para>
<para>
<literal>ABSOLUTE</literal> 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
<literal>FETCH ABSOLUTE 0</literal>) is fast.
</para>
<para>
Updating data via a cursor is currently not supported by
<productname>PostgreSQL</productname>.
</para>
<para>
<xref linkend="sql-declare" endterm="sql-declare-title">
is used to define a cursor. Use
<xref linkend="sql-move" endterm="sql-move-title">
to change cursor position without retrieving data.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
The following example traverses a table using a cursor.
<programlisting>
-- Set up and use a cursor:
BEGIN WORK;
-- Set up a cursor:
DECLARE liahona SCROLL CURSOR FOR SELECT * FROM films;
-- Fetch first 5 rows in the cursor liahona:
FETCH FORWARD 5 IN liahona;
-- Fetch the first 5 rows in the cursor liahona:
FETCH FORWARD 5 FROM liahona;
<computeroutput>
code | title | did | date_prod | kind | len
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
</computeroutput>
-- Fetch previous row:
-- Fetch the previous row:
FETCH PRIOR FROM liahona;
<computeroutput>
code | title | did | date_prod | kind | len
code | title | did | date_prod | kind | len
-------+---------+-----+------------+--------+-------
P_301 | Vertigo | 103 | 1958-11-14 | Action | 02:08
</computeroutput>
-- close the cursor and commit work:
-- Close the cursor and end the transaction:
CLOSE liahona;
COMMIT WORK;
</programlisting>
</para>
</refsect1>
<refsect1 id="R1-SQL-FETCH-3">
<title>
Compatibility
</title>
<refsect1>
<title>Compatibility</title>
<refsect2 id="R2-SQL-FETCH-4">
<refsect2info>
<date>2003-03-11</date>
</refsect2info>
<title>
SQL92
</title>
<para>
The SQL standard defines <command>FETCH</command> for use in
embedded SQL only. This variant of <command>FETCH</command>
described here returns the data as if it were a
<command>SELECT</command> result rather than placing it in host
variables. Other than this point, <command>FETCH</command> is
fully upward-compatible with the SQL standard.
</para>
<para>
<acronym>SQL92</acronym> defines <command>FETCH</command> for use
in embedded contexts only. Therefore, it describes placing the
results into explicit variables using an <literal>INTO</> clause,
for example:
<para>
The <command>FETCH</command> forms involving
<literal>FORWARD</literal> and <literal>BACKWARD</literal>, as well
as the forms <literal>FETCH <replaceable
class="PARAMETER">count</replaceable></literal> and <literal>FETCH
ALL</literal>, in which <literal>FORWARD</literal> is implicit, are
<productname>PostgreSQL</productname> extensions.
</para>
<synopsis>
FETCH ABSOLUTE <replaceable class="PARAMETER">n</replaceable>
FROM <replaceable class="PARAMETER">cursor</replaceable>
INTO :<replaceable class="PARAMETER">variable</replaceable> [, ...]
</synopsis>
<productname>PostgreSQL</productname>'s use of non-embedded
cursors is non-standard, and so is its practice of returning the
result data as if it were a <command>SELECT</command> result.
Other than this point, <command>FETCH</command> is fully
upward-compatible with <acronym>SQL92</acronym>.
</para>
<para>
The <command>FETCH</command> forms involving FORWARD and BACKWARD
(including the forms FETCH <replaceable
class="PARAMETER">count</replaceable> and FETCH ALL, in which
FORWARD is implicit) are <productname>PostgreSQL</productname>
extensions.
</para>
<para>
<acronym>SQL92</acronym> allows only <literal>FROM</> preceding the
cursor name; the option to use <literal>IN</> is an extension.
</para>
</refsect2>
<para>
The SQL standard allows only <literal>FROM</> preceding the cursor
name; the option to use <literal>IN</> is an extension.
</para>
</refsect1>
</refentry>