PostgreSQL Oracle 兼容性之 TABLE、PIPELINED函数

背景

Oracle 通过table, pipelined函数，用于格式化返回类型为table的函数的结果。

Table function concepts

There a couple of steps to take when you are working with table functions. Like when you are working with normal tables you have to describe the way the records of the collection are set up.

例子:

-- 定义复合类型  
CREATE TYPE script_line AS OBJECT  
(line NUMBER   ,text VARCHAR2(32767))  
  
-- 定义表类型  
CREATE or replace TYPE script_lines AS TABLE OF script_line;  
  
-- 定义返回表类型的函数  
CREATE OR REPLACE FUNCTION createinsertscriptfor(  
tablename_in IN VARCHAR2 ) RETURN script_lines  
....  
  
-- 通过TABLE格式化返回表类型的函数的结果集  
select * from TABLE(createinsertscriptfor('xx'));

pipelinedb的功能与table类似，不过它是流式返回，不需要等所有结果接收完后再格式化输出。

Functions can be pipelined. This means the results will become available when they are produced. As soon as a result is available instead of adding it to the nested table it will be piped out of the function.

例子:

CREATE OR REPLACE FUNCTION createinsertscriptfor(  
tablename_in IN VARCHAR2 ) RETURN script_lines PIPELINED  
.....

PostgreSQL TABLE、PIPELINED兼容性

1、PostgreSQL 建表时，自动建立对应的表类型、表数组类型。

例子

postgres=# create table abc(id int, info text);  
CREATE TABLE  
  
自动建立对应的复合类型以及复合数组类型。  
postgres=# select * from pg_type where typname ~ 'abc';  
 typname | typnamespace | typowner | typlen | typbyval | typtype | typcategory | typispreferred | typisdefined | typdelim | typrelid | typelem | typarray | typinput  | typoutput  | typreceive  |   typsend   | typmodin | typmodout |    ty  
panalyze    | typalign | typstorage | typnotnull | typbasetype | typtypmod | typndims | typcollation | typdefaultbin | typdefault | typacl   
---------+--------------+----------+--------+----------+---------+-------------+----------------+--------------+----------+----------+---------+----------+-----------+------------+-------------+-------------+----------+-----------+------  
------------+----------+------------+------------+-------------+-----------+----------+--------------+---------------+------------+--------  
 abc     |        34201 |       10 |     -1 | f        | c       | C           | f              | t            | ,        |    34634 |       0 |    34635 | record_in | record_out | record_recv | record_send | -        | -         | -      
            | d        | x          | f          |           0 |        -1 |        0 |            0 |               |            |   
 _abc    |        34201 |       10 |     -1 | f        | b       | A           | f              | t            | ,        |        0 |   34636 |        0 | array_in  | array_out  | array_recv  | array_send  | -        | -         | array  
_typanalyze | d        | x          | f          |           0 |        -1 |        0 |            0 |               |            |   
(2 rows)  
  
将一个字符串转换为复合类型  
  
postgres=# select '(1,hello)'::abc;  
    abc      
-----------  
 (1,hello)  
(1 row)  
  
postgres=# select ('(1,hello)'::abc).id;  
 id   
----  
  1  
(1 row)  
  
postgres=# select ('(1,hello)'::abc).info;  
 info    
-------  
 hello  
(1 row)  
  
删表后自动删除  
  
postgres=# drop table abc;  
DROP TABLE  
postgres=# select * from pg_type where typname ~ 'abc';  
 typname | typnamespace | typowner | typlen | typbyval | typtype | typcategory | typispreferred | typisdefined | typdelim | typrelid | typelem | typarray | typinput | typoutput | typreceive | typsend | typmodin | typmodout | typanalyze |  
 typalign | typstorage | typnotnull | typbasetype | typtypmod | typndims | typcollation | typdefaultbin | typdefault | typacl   
---------+--------------+----------+--------+----------+---------+-------------+----------------+--------------+----------+----------+---------+----------+----------+-----------+------------+---------+----------+-----------+------------+  
----------+------------+------------+-------------+-----------+----------+--------------+---------------+------------+--------  
(0 rows)

2、PostgreSQL 支持自定义复合类型，定义复合类型时，自动建立对应的复合数组类型。

例子

postgres=# create type typ1 as (id int, c1 int, c2 date);  
CREATE TYPE  
postgres=# select * from pg_type where typname ~ 'typ1';  
 typname | typnamespace | typowner | typlen | typbyval | typtype | typcategory | typispreferred | typisdefined | typdelim | typrelid | typelem | typarray | typinput  | typoutput  | typreceive  |   typsend   | typmodin | typmodout |    ty  
panalyze    | typalign | typstorage | typnotnull | typbasetype | typtypmod | typndims | typcollation | typdefaultbin | typdefault | typacl   
---------+--------------+----------+--------+----------+---------+-------------+----------------+--------------+----------+----------+---------+----------+-----------+------------+-------------+-------------+----------+-----------+------  
------------+----------+------------+------------+-------------+-----------+----------+--------------+---------------+------------+--------  
 typ1    |        34201 |       10 |     -1 | f        | c       | C           | f              | t            | ,        |    34646 |       0 |    34647 | record_in | record_out | record_recv | record_send | -        | -         | -      
            | d        | x          | f          |           0 |        -1 |        0 |            0 |               |            |   
 _typ1   |        34201 |       10 |     -1 | f        | b       | A           | f              | t            | ,        |        0 |   34648 |        0 | array_in  | array_out  | array_recv  | array_send  | -        | -         | array  
_typanalyze | d        | x          | f          |           0 |        -1 |        0 |            0 |               |            |   
(2 rows)  
  
将一个字符串转换为复合类型  
  
postgres=# select '(1,2,20170901)'::typ1;  
       typ1         
------------------  
 (1,2,2017-09-01)  
(1 row)  
  
postgres=# select ('(1,2,20170901)'::typ1).*;  
 id | c1 |     c2       
----+----+------------  
  1 |  2 | 2017-09-01  
(1 row)

3、PostgreSQL 函数支持返回不定义结构的类型record，或者定义结构的类型table, type, comp type等。

例子1，返回record，在查询时对其结构化。

create or replace function ftest1() returns record as $$  
declare  
begin  
  return (1,2,3,4);  
end;  
$$ language plpgsql strict;  
  
postgres=# select * from ftest1() as t(c1 int, c2 int, c3 int, c4 int);  
 c1 | c2 | c3 | c4   
----+----+----+----  
  1 |  2 |  3 |  4  
(1 row)

例子2，返回record，同时定义OUT参数，在查询时无需结构化。

postgres=# DROP FUNCTION ftest1();  
DROP FUNCTION  
postgres=# create or replace function ftest1(OUT C1 INT, OUT C2 TEXT) returns RECORD as $$  
declare  
begin  
  c1:=1;   
  c2:='abcde';   
  return;  
end;  
$$ language plpgsql strict;  
CREATE FUNCTION  
  
postgres=# select * from ftest1();  
 c1 |  c2     
----+-------  
  1 | abcde  
(1 row)

例子，返回table，在查询时无需结构化

postgres=# create table abcd(id int, info text);  
CREATE TABLE  
  
postgres=# create or replace function ftest2() returns abcd as $$  
declare  
begin  
  return (1, 'hello')::abcd;  
end;  
$$ language plpgsql strict;  
CREATE FUNCTION  
  
postgres=# select * from ftest2();  
 id | info    
----+-------  
  1 | hello  
(1 row)

4、PostgreSQL 函数支持返回数组。

例子

postgres=# create or replace function ftest3() returns abcd[] as $$  
declare   
  res abcd[];  
begin  
  res := array[(1, 'hello')::abcd];   
  res := array_cat(res, array[(2,'digoal')::abcd]);  
  return res;   
end;  
$$ language plpgsql strict;  
CREATE FUNCTION  
  
postgres=# select * from ftest3();  
           ftest3             
----------------------------  
 {"(1,hello)","(2,digoal)"}  
(1 row)

5、PostgreSQL 函数支持返回多条记录。

例子

postgres=# create or replace function ftest4() returns setof abcd[] as $$  
declare   
  res abcd[];  
begin  
  res := array[(1, 'hello')::abcd];   
  res := array_cat(res, array[(2,'digoal')::abcd]);  
  return next res;   
  return next array_cat(res,res);   
  return;   
end;  
$$ language plpgsql strict;  
CREATE FUNCTION  
  
postgres=# select * from ftest4();  
                       ftest4                          
-----------------------------------------------------  
 {"(1,hello)","(2,digoal)"}  
 {"(1,hello)","(2,digoal)","(1,hello)","(2,digoal)"}  
(2 rows)

6、PostgreSQL 函数支持返回游标（对应Oracle pipeline流式返回）。

postgres=# create or replace function ftest5() returns refcursor as $$  
declare  
  res refcursor := 'cur_1';  
begin   
  open res for select relname, relkind, relpages from pg_class ;  
  return res;  
end;  
$$ language plpgsql strict;  
CREATE FUNCTION  
  
  
postgres=# begin;  
BEGIN  
postgres=# select * from ftest5();  
 ftest5   
--------  
 cur_1  
(1 row)  
  
postgres=# fetch next from cur_1;  
 relname | relkind | relpages   
---------+---------+----------  
 seq     | S       |        1  
(1 row)  
  
postgres=# fetch next from cur_1;  
      relname      | relkind | relpages   
-------------------+---------+----------  
 idx_train_order_1 | i       |        1  
(1 row)