| Документация по PostgreSQL 9.1.1 | ||||
|---|---|---|---|---|
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This section describes functions that possibly return more than one row. Currently the only functions in this class are series generating functions, as detailed in Table 9-45 and Table 9-46.
Table 9-45. Series Generating Functions
| Function | Argument Type | Return Type | Description |
|---|---|---|---|
generate_series(start, stop) | int or bigint | setof int or setof bigint (same as argument type) | Generate a series of values, from start to stop with a step size of one |
generate_series(start, stop, step) | int or bigint | setof int or setof bigint (same as argument type) | Generate a series of values, from start to stop with a step size of step |
generate_series(start, stop, step interval) | timestamp or timestamp with time zone | setof timestamp or setof timestamp with time zone (same as argument type) | Generate a series of values, from start to stop with a step size of step |
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 for NULL inputs. 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)
-- 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)
Table 9-46. Subscript Generating Functions
| Function | Return Type | Description |
|---|---|---|
generate_subscripts(array anyarray, dim int) | setof int | Generate a series comprising the given array's subscripts. |
generate_subscripts(array anyarray, dim int, reverse boolean) | setof int | Generate a series comprising the given array's subscripts. When reverse is true, the series is returned 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 for NULL arrays (but valid subscripts are returned for NULL array
elements). 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
postgres=# SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
unnest2
---------
1
2
3
4
(4 rows)