FETCHNameFETCH -- retrieve rows from a query using a cursor SynopsisFETCH [ direction { FROM | IN } ] cursorname
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 Description 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
retrieved. If 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 FETCH BACKWARD
ALL will always leave the cursor positioned after the last row or before
the first row.
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.
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 count exceeds the number of rows
available).
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.
Parameters- direction
direction defines
the fetch direction and number of rows to fetch. It can be one
of the following:
- NEXT
Fetch the next row. This is the default if direction is omitted.
- PRIOR
Fetch the prior row.
- FIRST
Fetch the first row of the query (same as ABSOLUTE 1).
- LAST
Fetch the last row of the query (same as ABSOLUTE -1).
- ABSOLUTE count
Fetch the count'th row of the query,
or the 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 0 positions before
the first row.
- RELATIVE count
Fetch the count'th succeeding row, or
the abs(count)'th prior
row if count is
negative. RELATIVE 0 re-fetches the
current row, if any.
- count
Fetch the next count rows (same as
FORWARD count).
- ALL
Fetch all remaining rows (same as FORWARD ALL).
- FORWARD
Fetch the next row (same as NEXT).
- FORWARD count
Fetch the next count rows.
FORWARD 0 re-fetches the current row.
- FORWARD ALL
Fetch all remaining rows.
- BACKWARD
Fetch the prior row (same as PRIOR).
- BACKWARD count
Fetch the prior count rows (scanning
backwards). BACKWARD 0 re-fetches the
current row.
- BACKWARD ALL
Fetch all prior rows (scanning backwards).
- count
count is a
possibly-signed integer constant, determining the location or
number of rows to fetch. For FORWARD and
BACKWARD cases, specifying a negative count is equivalent to changing
the sense of FORWARD and BACKWARD.
- cursorname
An open cursor's name.
Outputs On successful completion, a FETCH command returns a command
tag of the form
FETCH count
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.
Notes The cursor should be declared with the SCROLL
option if one intends to use any variants of FETCH
other than FETCH NEXT or FETCH FORWARD with
a positive count. For simple queries
EnterpriseDB 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.
Updating data via a cursor is currently not supported by
EnterpriseDB.
DECLARE
is used to define a cursor.
Examples 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;
Compatibility The SQL standard defines FETCH for use in
embedded SQL only. The variant of FETCH
described here returns the data as if it were a
SELECT result rather than placing it in host
variables. Other than this point, FETCH is
fully upward-compatible with the SQL standard.
The FETCH forms involving
FORWARD and BACKWARD, as well
as the forms FETCH count and FETCH
ALL, in which FORWARD is implicit, are
EnterpriseDB extensions.
The SQL standard allows only FROM preceding the cursor
name; the option to use IN is an extension.
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