【原创】PostgreSQL 遍历表的PLSQL列举
我们经常会对数据字典中的系统表进行遍历，从而写一些SHELL脚本或者动态造数据等等。 这里我用PLSQL演示了三种方法来遍历一张表。表结构如下，
[*]t_girl=# \d tmp_1;
[*] Unlogged table "public.tmp_1"
[*]Column | Type | Modifiers
[*]----------+-----------------------------+-----------
[*] id | integer |
[*] log_time | timestamp without time zone |
在这里我创建里一个自定义类型来保存我的函数返回值。
[*]create type ytt_record as (id int,log_time timestamp without time zone);
现在来看第一个函数。 也是用最笨的方法来遍历。
[*]create or replace function sp_test_record1(
[*]IN f_id int
[*]) returns setof ytt_record as
[*]$ytt$
[*]declare i int;
[*]declare cnt int;
[*]
[*]
[*]declare o_out ytt_record;
[*]begin
[*] i := 0;
[*] cnt := 0;
[*] select count(*) into cnt from tmp_1 where id > f_id;
[*] while i f_id order by log_time desc limit 1 offset i;
[*] i := i + 1;
[*] return next o_out;
[*] end loop;
[*]end;
[*]$ytt$ language plpgsql;
我们来执行下结果，花费了3毫秒左右。
[*]t_girl=# select * from sp_test_record1(60);
[*] id | log_time
[*]----+----------------------------
[*] 85 | 2014-01-11 17:52:11.696354
[*] 73 | 2014-01-09 17:52:11.696354
[*] 77 | 2014-01-04 17:52:11.696354
[*] 80 | 2014-01-03 17:52:11.696354
[*] 76 | 2014-01-02 17:52:11.696354
[*] 65 | 2013-12-31 17:52:11.696354
[*] 80 | 2013-12-30 17:52:11.098336
[*] 85 | 2013-12-27 17:52:11.098336
[*] 97 | 2013-12-26 17:52:11.696354
[*] 94 | 2013-12-24 17:52:09.321394
[*](10 rows)
[*]
[*]
[*]Time: 3.338 ms
现在来看第二个函数，这个就比较优化了， 用了系统自带的循环遍历结构。
[*]create or replace function sp_test_record2(
[*]IN f_id int
[*]) returns setof ytt_record as
[*]$ytt$
[*]
[*]
[*]declare o_out ytt_record;
[*]begin
[*]
[*]
[*]for o_out in select id,log_time from tmp_1 where id > f_id order by log_time desc
[*]loop
[*] return next o_out;
[*] end loop;
[*]end;
[*]$ytt$ language plpgsql;
这次运行结果看看，时间不到1毫秒。
[*]t_girl=# select * from sp_test_record2(60);
[*] id | log_time
[*]----+----------------------------
[*] 85 | 2014-01-11 17:52:11.696354
[*] 73 | 2014-01-09 17:52:11.696354
[*] 77 | 2014-01-04 17:52:11.696354
[*] 80 | 2014-01-03 17:52:11.696354
[*] 76 | 2014-01-02 17:52:11.696354
[*] 65 | 2013-12-31 17:52:11.696354
[*] 80 | 2013-12-30 17:52:11.098336
[*] 85 | 2013-12-27 17:52:11.098336
[*] 97 | 2013-12-26 17:52:11.696354
[*] 94 | 2013-12-24 17:52:09.321394
[*](10 rows)
[*]
[*]
[*]Time: 0.660 ms
最后一个函数， 利用RETURN QUERY 直接返回结果集。
[*]create or replace function sp_test_record3(
[*]IN f_id int
[*]) returns setof ytt_record as
[*]$ytt$
[*]
[*]
[*]begin
[*]return query select id,log_time from tmp_1 where id > f_id order by log_time desc ;
[*]end;
[*]$ytt$ language plpgsql;
这个结果其实等同于直接从表SELECT，响应时间和第二个差不多。
[*]t_girl=# select sp_test_record3(60);
[*] sp_test_record3
[*]-----------------------------------
[*] (85,"2014-01-11 17:52:11.696354")
[*] (73,"2014-01-09 17:52:11.696354")
[*] (77,"2014-01-04 17:52:11.696354")
[*] (80,"2014-01-03 17:52:11.696354")
[*] (76,"2014-01-02 17:52:11.696354")
[*] (65,"2013-12-31 17:52:11.696354")
[*] (80,"2013-12-30 17:52:11.098336")
[*] (85,"2013-12-27 17:52:11.098336")
[*] (97,"2013-12-26 17:52:11.696354")
[*] (94,"2013-12-24 17:52:09.321394")
[*](10 rows)
[*]
[*]
[*]Time: 0.877 ms
[*]t_girl=#
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