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9.26. Set Returning Functions

9.26. Set Returning Functions
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This section describes functions that possibly return more than one row. The most widely used functions in this class are series generating functions, as detailed in Table 9.67 and Table 9.68 . Other, more specialized set-returning functions are described elsewhere in this manual. See Section 7.2.1.4 for ways to combine multiple set-returning functions.

Table 9.67. Series Generating Functions

Function

Description

generate_series ( start integer , stop integer [ , step integer ] ) → setof integer

generate_series ( start bigint , stop bigint [ , step bigint ] ) → setof bigint

generate_series ( start numeric , stop numeric [ , step numeric ] ) → setof numeric

Generates a series of values from start to stop , with a step size of step . step defaults to 1.

generate_series ( start timestamp , stop timestamp , step interval ) → setof timestamp

generate_series ( start timestamp with time zone , stop timestamp with time zone , step interval [ , timezone text ] ) → setof timestamp with time zone

Generates a series of values from start to stop , with a step size of step . In the timezone-aware form, times of day and daylight-savings adjustments are computed according to the time zone named by the timezone argument, or the current TimeZone setting if that is omitted.


When step is positive, zero rows are returned if start is greater than stop . Conversely, when step is negative, zero rows are returned if start is less than stop . Zero rows are also returned if any input is NULL . It is an error for step to be zero. Some examples follow: 

SELECT * FROM generate_series(2,4);
 generate_series
-----------------
               2
               3
               4
(3 rows)

SELECT * FROM generate_series(5,1,-2);
 generate_series
-----------------
               5
               3
               1
(3 rows)

SELECT * FROM generate_series(4,3);
 generate_series
-----------------
(0 rows)

SELECT generate_series(1.1, 4, 1.3);
 generate_series
-----------------
             1.1
             2.4
             3.7
(3 rows)

-- this example relies on the date-plus-integer operator:
SELECT current_date + s.a AS dates FROM generate_series(0,14,7) AS s(a);
   dates
------------
 2004-02-05
 2004-02-12
 2004-02-19
(3 rows)

SELECT * FROM generate_series('2008-03-01 00:00'::timestamp,
                              '2008-03-04 12:00', '10 hours');
   generate_series
---------------------
 2008-03-01 00:00:00
 2008-03-01 10:00:00
 2008-03-01 20:00:00
 2008-03-02 06:00:00
 2008-03-02 16:00:00
 2008-03-03 02:00:00
 2008-03-03 12:00:00
 2008-03-03 22:00:00
 2008-03-04 08:00:00
(9 rows)

-- this example assumes that TimeZone is set to UTC; note the DST transition:
SELECT * FROM generate_series('2001-10-22 00:00 -04:00'::timestamptz,
                              '2001-11-01 00:00 -05:00'::timestamptz,
                              '1 day'::interval, 'America/New_York');
    generate_series
------------------------
 2001-10-22 04:00:00+00
 2001-10-23 04:00:00+00
 2001-10-24 04:00:00+00
 2001-10-25 04:00:00+00
 2001-10-26 04:00:00+00
 2001-10-27 04:00:00+00
 2001-10-28 04:00:00+00
 2001-10-29 05:00:00+00
 2001-10-30 05:00:00+00
 2001-10-31 05:00:00+00
 2001-11-01 05:00:00+00
(11 rows)

Table 9.68. Subscript Generating Functions

Function

Description

generate_subscripts ( array anyarray , dim integer ) → setof integer

Generates a series comprising the valid subscripts of the dim 'th dimension of the given array.

generate_subscripts ( array anyarray , dim integer , reverse boolean ) → setof integer

Generates a series comprising the valid subscripts of the dim 'th dimension of the given array. When reverse is true, returns the series in reverse order.


generate_subscripts is a convenience function that generates the set of valid subscripts for the specified dimension of the given array. Zero rows are returned for arrays that do not have the requested dimension, or if any input is NULL . Some examples follow: 

-- basic usage:
SELECT generate_subscripts('{NULL,1,NULL,2}'::int[], 1) AS s;
 s
---
 1
 2
 3
 4
(4 rows)

-- presenting an array, the subscript and the subscripted
-- value requires a subquery:
SELECT * FROM arrays;
         a
--------------------
 {-1,-2}
 {100,200,300}
(2 rows)

SELECT a AS array, s AS subscript, a[s] AS value
FROM (SELECT generate_subscripts(a, 1) AS s, a FROM arrays) foo;
     array     | subscript | value
---------------+-----------+-------
 {-1,-2}       |         1 |    -1
 {-1,-2}       |         2 |    -2
 {100,200,300} |         1 |   100
 {100,200,300} |         2 |   200
 {100,200,300} |         3 |   300
(5 rows)

-- unnest a 2D array:
CREATE OR REPLACE FUNCTION unnest2(anyarray)
RETURNS SETOF anyelement AS $$
select $1[i][j]
   from generate_subscripts($1,1) g1(i),
        generate_subscripts($1,2) g2(j);
$$ LANGUAGE sql IMMUTABLE;
CREATE FUNCTION
SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
 unnest2
---------
       1
       2
       3
       4
(4 rows)

When a function in the FROM clause is suffixed by WITH ORDINALITY , a bigint column is appended to the function's output column(s), which starts from 1 and increments by 1 for each row of the function's output. This is most useful in the case of set returning functions such as unnest() . 

-- set returning function WITH ORDINALITY:
SELECT * FROM pg_ls_dir('.') WITH ORDINALITY AS t(ls,n);
       ls        | n
-----------------+----
 pg_serial       |  1
 pg_twophase     |  2
 postmaster.opts |  3
 pg_notify       |  4
 postgresql.conf |  5
 pg_tblspc       |  6
 logfile         |  7
 base            |  8
 postmaster.pid  |  9
 pg_ident.conf   | 10
 global          | 11
 pg_xact         | 12
 pg_snapshots    | 13
 pg_multixact    | 14
 PG_VERSION      | 15
 pg_wal          | 16
 pg_hba.conf     | 17
 pg_stat_tmp     | 18
 pg_subtrans     | 19
(19 rows)

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