PostgreSQL 遍历表的PLSQL列举

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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 mst_girl=#

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