# 9.25. 集合回傳函數
本節介紹可以回傳多筆資料的函數。 此類中使用最廣泛的函數是序列生成函數，詳見 [Table 9.64](#table-9.64.-series-generating-functions) 和 [Table 9.65](#table-9.65.-subscript-generating-functions)。 還有其他更有用的集合回傳函數也描述在本手冊的其他地方。 請參閱[第 7.2.1.4 節](https://docs.postgresql.tw/15/queries/table-expressions#7.2.1.4.-zi-liao-biao-han-shu)以了解組合多個集合傳回函數的方法。
#### **Table 9.64. 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 ) → setof timestamp with time zone
Generates 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 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)
```
#### **Table 9.65. 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)
```