Question

我试图启动一个SQL函数，以便我可以在另一个查询中收集我不想要的部分ID列表。我已尝试使用PGAdmin的“函数”构建器开始，但我遇到语法错误，因此无法创建该函数。谁能告诉我这里做错了什么？一旦我能够启动该功能，我想我可以弄清楚剩下的。只需要弄清楚正确的声明语法（我更常用于MSSQL的事务SQL语法）

到目前为止，这是我的代码：

CREATE FUNCTION get_unused_part_ids() RETURNS integer[] AS
$BODY$DECLARE
  part_ids integer ARRAY;

BEGIN
  set part_ids = '{1,2,3,4}'
  select part_ids

END;$BODY$
LANGUAGE sql VOLATILE;

我期待的是一个整数数组，其值为1,2,3和4.

Answer 1

具有正确语法的示例函数：

CREATE FUNCTION get_unused_part_ids() RETURNS integer[] AS
$BODY$
DECLARE
    part_ids integer ARRAY;

BEGIN
    part_ids = '{1,2,3,4}';
    return part_ids;
END;
$BODY$ LANGUAGE plpgsql;

select * from get_unused_part_ids();

 get_unused_part_ids 
---------------------
 {1,2,3,4}
(1 row)

注意，您需要plpgsql函数来获取局部变量。

Answer 2

@klin的回复是正确的，我有一个建议。请改用SQL语言。在描述的情况下，PostgreSQL planner可以使用更好的计划。 PLpgSQL函数是规划器的黑盒子：

CREATE OR REPLACE FUNCTION public.foo1()
 RETURNS integer[]
 LANGUAGE plpgsql
AS $function$
BEGIN
  RETURN ARRAY[1,2,3,4];
END;
$function$

CREATE OR REPLACE FUNCTION public.foo2()
 RETURNS integer[]
 LANGUAGE sql
AS $function$
  SELECT ARRAY[1,2,3,4];
$function$

CREATE TABLE boo(a int);
INSERT INTO boo SELECT random()*10 FROM generate_series(1,10000);
ANALYZE boo;

postgres=# EXPLAIN ANALYZE SELECT * FROM boo WHERE a = ANY(foo1());
                                             QUERY PLAN                                               
═════════════════════════════════════════════════════════════════════════════════════════════════════
Seq Scan on boo  (cost=0.00..2770.00 rows=6145 width=4) (actual time=0.118..49.949 rows=4104 loops=1)
  Filter: (a = ANY (foo1()))
  Rows Removed by Filter: 5896
Planning time: 0.096 ms
Execution time: 50.900 ms
(5 rows)

Time: 51.771 ms
postgres=# EXPLAIN ANALYZE SELECT * FROM boo WHERE a = ANY(foo2());
                                            QUERY PLAN                                              
═══════════════════════════════════════════════════════════════════════════════════════════════════
Seq Scan on boo  (cost=0.00..195.00 rows=4104 width=4) (actual time=0.036..4.700 rows=4104 loops=1)
  Filter: (a = ANY ('{1,2,3,4}'::integer[]))
  Rows Removed by Filter: 5896
Planning time: 0.193 ms
Execution time: 5.254 ms
(5 rows)

使用SQL函数可以获得更好的结果估计。 SQL函数是一个宏 - 如果你使用SQL函数，那么它等同于直接编写的查询：

postgres=# EXPLAIN ANALYZE SELECT * FROM boo WHERE a = ANY(ARRAY[1,2,3,4]);
                                                QUERY PLAN                                              
═══════════════════════════════════════════════════════════════════════════════════════════════════
Seq Scan on boo  (cost=0.00..195.00 rows=4104 width=4) (actual time=0.032..4.782 rows=4104 loops=1)
  Filter: (a = ANY ('{1,2,3,4}'::integer[]))
  Rows Removed by Filter: 5896
Planning time: 0.122 ms
Execution time: 5.325 ms
(5 rows)

在这种情况下，优化器具有更多信息并且可以使用它。对于具有常量结果的函数，SQL函数通常更好。

带整数数组的PL / pgSQL函数语法

2 个答案: