【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=#\\dtmp_1;U

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 < cnt loop select id,log_time into strict o_out from tmp_1 where id > 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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