Pg中有一个很有用处的内置函数generate_series,可以按不同的规则用来产生一系列的填充数据。

一、语法

generate_series(start,stop)                --int or bigint
generate_series(start,stop,step)           --int or bigint
generate_series(start,stop, step interval) --timestamp or timestamp with time zone

二、应用例子

1.int类型,不写步长时默认是1
postgres=# select generate_series(1,10);generate_series
-----------------12345678910
(10 rows)postgres=# select generate_series(1,10,3);generate_series
-----------------14710
(4 rows)postgres=# select generate_series(5,1);generate_series
-----------------
(0 rows)postgres=# select generate_series(5,1,-1);generate_series
-----------------54321
(5 rows) 2.时间类型
postgres=# select generate_series(now(),now() + '7 day','1 day');generate_series
-------------------------------2012-08-27 22:12:40.915368+082012-08-28 22:12:40.915368+082012-08-29 22:12:40.915368+082012-08-30 22:12:40.915368+082012-08-31 22:12:40.915368+082012-09-01 22:12:40.915368+082012-09-02 22:12:40.915368+082012-09-03 22:12:40.915368+08
(8 rows)postgres=# select generate_series(to_date('20120827','yyyymmdd'),to_date('20120828','yyyymmdd'),'3 h');generate_series
------------------------2012-08-27 00:00:00+082012-08-27 03:00:00+082012-08-27 06:00:00+082012-08-27 09:00:00+082012-08-27 12:00:00+082012-08-27 15:00:00+082012-08-27 18:00:00+082012-08-27 21:00:00+082012-08-28 00:00:00+08
(9 rows)3.IP类型
postgres=# create table t_kenyon(id int,ip_start inet,ip_end inet);
CREATE TABLE
postgres=# insert into t_kenyon values(1,'192.168.1.254','192.168.2.5');
INSERT 0 1
postgres=# insert into t_kenyon values(2,'192.168.2.254','192.168.3.5');
INSERT 0 1
postgres=# insert into t_kenyon values(3,'192.168.3.254','192.168.4.5');
INSERT 0 1postgres=# select * from t_kenyon;id |   ip_start    |   ip_end
----+---------------+-------------1 | 192.168.1.254 | 192.168.2.52 | 192.168.2.254 | 192.168.3.53 | 192.168.3.254 | 192.168.4.5
(3 rows)postgres=# select id,generate_series(0,ip_end-ip_start)+ip_start as ip_new from t_kenyon;id |    ip_new
----+---------------1 | 192.168.1.2541 | 192.168.1.2551 | 192.168.2.01 | 192.168.2.11 | 192.168.2.21 | 192.168.2.31 | 192.168.2.41 | 192.168.2.52 | 192.168.2.2542 | 192.168.2.2552 | 192.168.3.02 | 192.168.3.12 | 192.168.3.22 | 192.168.3.32 | 192.168.3.42 | 192.168.3.53 | 192.168.3.2543 | 192.168.3.2553 | 192.168.4.03 | 192.168.4.13 | 192.168.4.23 | 192.168.4.33 | 192.168.4.43 | 192.168.4.5
(24 rows)

三、总结
Pg的generate_series函数对生成测试数据,批量更新一定规则的数据有比较多的应用场景，使用得当可提升开发效率。另外IP的序列生成也是PG的一个亮点。
有两种情况不能生成数据：
1.步长为正,且开始值比结束值大
2.步长为负,且开始值比结束值小

四、参考：
http://www.postgresql.org/docs/9.0/static/functions-srf.html http://blog.163.com/digoal@126/blog/static/163877040201111805555263/