9.24. 集合回傳函式

Table 9.61. Series Generating Functions

 Function Argument Type Return Type Description `generate_series(``start`, `stop`) `int`, `bigint` or `numeric` `setof int`, `setof bigint`, or `setof numeric` (same as argument type) 從 start 到 stop 產生成一系列的值，間隔為 1 `generate_series(``start`, `stop`, `step`) `int`, `bigint` or `numeric` `setof int`, `setof bigint` or `setof numeric` (same as argument type) 產生一系列的值，從 start 到 end，間隔為 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) 產生一系列的值，從 start 到 end，間隔為 step

``````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 9.62. Subscript Generating Functions

 Function Return Type Description `generate_subscripts(``array anyarray`, `dim int`) `setof int` 產生成一個包含給定陣列索引的系列內容。 `generate_subscripts(``array anyarray`, `dim int`, `reverse boolean`) `setof int` 產生一個包含給定陣列索引的序列內容。當 reverse 為 true 時，將以相反的順序回傳該序列。

generate_subscripts 是一個很方便的函數，用於為給定陣列的指定維度產成一組有效的索引內容。對於沒有所請求維數的陣列或 NULL 陣列，回傳零筆資料（但是對於 NULL 陣列元素，回傳有效的索引）。以下是一些範例：

``````-- 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)``````

``````-- 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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