Current File : //opt/alt/postgresql11/usr/share/man/man7/FETCH.7
'\" t
.\" Title: FETCH
.\" Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\" Date: 2017-11-06
.\" Manual: PostgreSQL 9.2.24 Documentation
.\" Source: PostgreSQL 9.2.24
.\" Language: English
.\"
.TH "FETCH" "7" "2017-11-06" "PostgreSQL 9.2.24" "PostgreSQL 9.2.24 Documentation"
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.SH "NAME"
FETCH \- retrieve rows from a query using a cursor
.\" FETCH
.\" cursor: FETCH
.SH "SYNOPSIS"
.sp
.nf
FETCH [ \fIdirection\fR [ FROM | IN ] ] \fIcursor_name\fR
where \fIdirection\fR can be empty or one of:
NEXT
PRIOR
FIRST
LAST
ABSOLUTE \fIcount\fR
RELATIVE \fIcount\fR
\fIcount\fR
ALL
FORWARD
FORWARD \fIcount\fR
FORWARD ALL
BACKWARD
BACKWARD \fIcount\fR
BACKWARD ALL
.fi
.SH "DESCRIPTION"
.PP
\fBFETCH\fR
retrieves rows using a previously\-created cursor\&.
.PP
A cursor has an associated position, which is used by
\fBFETCH\fR\&. 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
\fBFETCH\fR
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\&.
\fBFETCH ALL\fR
or
\fBFETCH BACKWARD ALL\fR
will always leave the cursor positioned after the last row or before the first row\&.
.PP
The 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\&.
.PP
The forms using
FORWARD
and
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
\fIcount\fR
exceeds the number of rows available)\&.
.PP
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\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
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.br
.ps +1
\fBNote\fR
.ps -1
.br
.PP
This page describes usage of cursors at the SQL command level\&. If you are trying to use cursors inside a
PL/pgSQL
function, the rules are different \(em see
Section 39.7, \(lqCursors\(rq, in the documentation\&.
.sp .5v
.RE
.SH "PARAMETERS"
.PP
\fIdirection\fR
.RS 4
\fIdirection\fR
defines the fetch direction and number of rows to fetch\&. It can be one of the following:
.PP
NEXT
.RS 4
Fetch the next row\&. This is the default if
\fIdirection\fR
is omitted\&.
.RE
.PP
PRIOR
.RS 4
Fetch the prior row\&.
.RE
.PP
FIRST
.RS 4
Fetch the first row of the query (same as
ABSOLUTE 1)\&.
.RE
.PP
LAST
.RS 4
Fetch the last row of the query (same as
ABSOLUTE \-1)\&.
.RE
.PP
ABSOLUTE \fIcount\fR
.RS 4
Fetch the
\fIcount\fR\*(Aqth row of the query, or the
abs(\fIcount\fR)\*(Aqth row from the end if
\fIcount\fR
is negative\&. Position before first row or after last row if
\fIcount\fR
is out of range; in particular,
ABSOLUTE 0
positions before the first row\&.
.RE
.PP
RELATIVE \fIcount\fR
.RS 4
Fetch the
\fIcount\fR\*(Aqth succeeding row, or the
abs(\fIcount\fR)\*(Aqth prior row if
\fIcount\fR
is negative\&.
RELATIVE 0
re\-fetches the current row, if any\&.
.RE
.PP
\fIcount\fR
.RS 4
Fetch the next
\fIcount\fR
rows (same as
FORWARD \fIcount\fR)\&.
.RE
.PP
ALL
.RS 4
Fetch all remaining rows (same as
FORWARD ALL)\&.
.RE
.PP
FORWARD
.RS 4
Fetch the next row (same as
NEXT)\&.
.RE
.PP
FORWARD \fIcount\fR
.RS 4
Fetch the next
\fIcount\fR
rows\&.
FORWARD 0
re\-fetches the current row\&.
.RE
.PP
FORWARD ALL
.RS 4
Fetch all remaining rows\&.
.RE
.PP
BACKWARD
.RS 4
Fetch the prior row (same as
PRIOR)\&.
.RE
.PP
BACKWARD \fIcount\fR
.RS 4
Fetch the prior
\fIcount\fR
rows (scanning backwards)\&.
BACKWARD 0
re\-fetches the current row\&.
.RE
.PP
BACKWARD ALL
.RS 4
Fetch all prior rows (scanning backwards)\&.
.RE
.RE
.PP
\fIcount\fR
.RS 4
\fIcount\fR
is a possibly\-signed integer constant, determining the location or number of rows to fetch\&. For
FORWARD
and
BACKWARD
cases, specifying a negative
\fIcount\fR
is equivalent to changing the sense of
FORWARD
and
BACKWARD\&.
.RE
.PP
\fIcursor_name\fR
.RS 4
An open cursor\*(Aqs name\&.
.RE
.SH "OUTPUTS"
.PP
On successful completion, a
\fBFETCH\fR
command returns a command tag of the form
.sp
.if n \{\
.RS 4
.\}
.nf
FETCH \fIcount\fR
.fi
.if n \{\
.RE
.\}
.sp
The
\fIcount\fR
is the number of rows fetched (possibly zero)\&. Note that in
psql, the command tag will not actually be displayed, since
psql
displays the fetched rows instead\&.
.SH "NOTES"
.PP
The cursor should be declared with the
SCROLL
option if one intends to use any variants of
\fBFETCH\fR
other than
\fBFETCH NEXT\fR
or
\fBFETCH FORWARD\fR
with a positive count\&. For simple queries
PostgreSQL
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\&.
.PP
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\&.
.PP
\fBDECLARE\fR(7)
is used to define a cursor\&. Use
\fBMOVE\fR(7)
to change cursor position without retrieving data\&.
.SH "EXAMPLES"
.PP
The following example traverses a table using a cursor:
.sp
.if n \{\
.RS 4
.\}
.nf
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;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
The SQL standard defines
\fBFETCH\fR
for use in embedded SQL only\&. The variant of
\fBFETCH\fR
described here returns the data as if it were a
\fBSELECT\fR
result rather than placing it in host variables\&. Other than this point,
\fBFETCH\fR
is fully upward\-compatible with the SQL standard\&.
.PP
The
\fBFETCH\fR
forms involving
FORWARD
and
BACKWARD, as well as the forms
FETCH \fIcount\fR
and
FETCH ALL, in which
FORWARD
is implicit, are
PostgreSQL
extensions\&.
.PP
The SQL standard allows only
FROM
preceding the cursor name; the option to use
IN, or to leave them out altogether, is an extension\&.
.SH "SEE ALSO"
\fBCLOSE\fR(7), \fBDECLARE\fR(7), \fBMOVE\fR(7)
Mini Shell