Postgresql 中文操作指南

9.25. Set Returning Functions #

本节介绍了可能返回多行的函数。此类中最广泛使用的函数是序列生成函数，如 Table 9.65和 Table 9.66中所述。本手册其他地方介绍了其他更专门的返回集的函数。有关如何组合多个返回集合的函数，请参见 Section 7.2.1.4。

Table 9.65. 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 从 start 到 stop 生成一系列值，步长为 step 。默认情况下 step 为 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 从 start 到 stop 生成一系列值，步长为 step 。在时区感知形式中，会根据 timezone 参数命名的时区或（如果省略了 timezone 参数）当前 TimeZone 设置来计算时间和夏令时调整。

当 step 为正数时，若 start 大于 stop，则返回 0 行。相反，当 step 为负数时，若 start 小于 stop，则返回 0 行。若任何输入为 NULL，也将返回 0 行。step 为零将产生错误。以下是几个示例：

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 9.66. Subscript Generating Functions

Function

Description

generate_subscripts ( array anyarray , dim integer ) → setof integer 生成一个序列，包括给定数组的 dim 维度的有效下标。

generate_subscripts ( array anyarray , dim integer , reverse boolean ) → setof integer 生成一个序列，包括给定数组的 dim 维度的有效下标。当 reverse 为 true 时，以相反的顺序返回序列。

generate_subscripts 是一种便捷函数，用于生成所给数组指定维度中有效下标的集合。对于没有请求维度的数组，或任何输入为 NULL 的情况，将返回 0 行。以下是一些示例：

-- 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)

当 FROM 子句中的函数后缀为 WITH ORDINALITY 时，将一个 bigint 列附加到该函数的输出列（如果存在），该列从 1 开始，每个函数输出行增量 1。这在使用诸如 unnest() 等返回集合的函数时非常有用。

-- 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)