FETCH — retrieve rows from a query using a cursor
direction[ FROM | IN ] ]
directioncan be empty or one of: NEXT PRIOR FIRST LAST ABSOLUTE
countALL FORWARD FORWARD
countFORWARD ALL BACKWARD BACKWARD
FETCH retrieves rows using a
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 retrieved. If
off the end of the available rows then the cursor is left
positioned after the last row, or before the first row if
FETCH ALL or
FETCH BACKWARD ALL will always
leave the cursor positioned after the last row or before the
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 using
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
count exceeds the number of
FORWARD 0, and
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
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 Section 43.7.3.
defines 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
Fetch the prior row.
Fetch the first row of the query (same as
Fetch the last row of the query (same as
count'th row of the
query, or the
row from the end if
count is negative.
Position before first row or after last row if
out of range; in particular,
ABSOLUTE 0 positions before the
row, or the
prior row if
count is negative.
RELATIVE 0 re-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
FORWARD 0 re-fetches
the current row.
Fetch all remaining rows.
Fetch the prior row (same as
Fetch the prior
BACKWARD 0 re-fetches the current
Fetch all prior rows (scanning backwards).
count is a
possibly-signed integer constant, determining the
location or number of rows to fetch. For
BACKWARD cases, specifying a negative
equivalent to changing the sense of
An open cursor's name.
On successful completion, a
FETCH command returns a command tag of 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
The cursor should be declared with the
SCROLL option if one intends to use any
FETCH other than
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
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
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 | 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;
The SQL standard defines
for use in embedded SQL only. The variant of
FETCH described here returns the data as if it
SELECT result rather than
placing it in host variables. Other than this point,
FETCH is fully upward-compatible
with the SQL standard.
FETCH forms involving
BACKWARD, as well as the forms
FETCH ALL, in which
FORWARD is implicit, are PostgreSQL extensions.
The SQL standard allows only
FROM preceding the cursor name; the option to
IN, or to leave them out
altogether, is an extension.
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