FETCH

cursor

FETCH

FETCH

7

SQL - Language Statements

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

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.

> **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 MDASH see [???](#plpgsql-cursor-using).

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`.

cursor\_name

:   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 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.

[`DECLARE`](#sql-declare) is used to define a cursor. Use
[`MOVE`](#sql-move) to change cursor position without retrieving data.

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 PostgreSQL extensions.

The SQL standard allows only `FROM` preceding the cursor name; the
option to use `IN`, or to leave them out altogether, is an extension.

See Also
========
