|The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 488 pages
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FETCH -- retrieve rows from a query using a cursor
FETCH [ direction [ FROM | IN ] ] cursor_name where direction can be empty or one of: NEXT PRIOR FIRST LAST ABSOLUTE count RELATIVE count count ALL FORWARD FORWARD count FORWARD ALL BACKWARD BACKWARD count BACKWARD ALL
FETCH retrieves rows using a previously-created cursor.
A cursor has an associated position, which is used by
FETCH. 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
FETCH 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.
FETCH ALL or
ALL will always leave the cursor positioned after the last row or before
the first row.
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
The forms using
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 count exceeds the number of rows
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.
Note: 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--see Volume 2: Cursors.
the fetch direction and number of rows to fetch. It can be one
of the following:
- Fetch the next row. This is the default if direction is omitted.
- Fetch the prior row.
Fetch the first row of the query (same as
Fetch the last row of the query (same as
Fetch the count'th row of the query,
abs(count)'th row from the end if count is negative. Position before first row or after last row if count is out of range; in particular,
ABSOLUTE 0positions before the first row.
Fetch the count'th succeeding row, or
abs(count)'th prior row if count is negative.
RELATIVE 0re-fetches the current row, if any.
Fetch the next count rows (same as
Fetch all remaining rows (same as
Fetch the next row (same as
Fetch the next count rows.
FORWARD 0re-fetches the current row.
- Fetch all remaining rows.
Fetch the prior row (same as
Fetch the prior count rows (scanning
BACKWARD 0re-fetches the current row.
- Fetch all prior rows (scanning backwards).
count is a
possibly-signed integer constant, determining the location or
number of rows to fetch. For
BACKWARDcases, specifying a negative count is equivalent to changing the sense of
- An open cursor's name.
On successful completion, a
FETCH command returns a command
tag of the form
The count 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.
The cursor should be declared with the
option if one intends to use any variants of
FETCH NEXT or
FETCH FORWARD 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.
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.
The following example traverses a table using a cursor:
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 | -------+-------------------------+-----+------------+----------+ BL101 | The Third Man | 101 | 1949-12-23 | Drama | BL102 | The African Queen | 101 | 1951-08-11 | Romantic | JL201 | Une Femme est une Femme | 102 | 1961-03-12 | Romantic | P_301 | Vertigo | 103 | 1958-11-14 | Action | P_302 | Becket | 103 | 1964-02-03 | Drama | len ------- 01:44 01:43 01:25 02:08 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;
The SQL standard defines
FETCH for use in
embedded SQL only. The variant of
described here returns the data as if it were a
SELECT result rather than placing it in host
variables. Other than this point,
fully upward-compatible with the SQL standard.
FETCH forms involving
BACKWARD, as well
as the forms
FETCH count and
ALL, in which
FORWARD is implicit, are
The SQL standard allows only
FROM preceding the cursor
name; the option to use
IN, or to leave them out altogether, is
|ISBN 9781906966058||The PostgreSQL 9.0 Reference Manual - Volume 1B - SQL Command Reference||See the print edition|