Question

在PostgreSQL中，在同一个查询中多次调用同一个函数的最佳方法是什么？

示例：

SELECT a.id, 
       sum_one(a.id) AS "Sum_one",
       sum_two(a.id) AS "Sum_two",
       (sum_one(a.id )+sum_two(a.id)) AS "Sum_three"
  FROM a

sum_one()和sum_two()是函数。我重复sum_one()和sum_two()的来电。这将减慢大型数据库中的查询速度。

我想避免以下声明。

(sum_one(a.id )+sum_two(a.id)) AS "Sum_three"

我怎么能在PostgreSQL中做到这一点？

Answer 1

您应将功能波动率设置为Stable。

More about function volatility

CREATE OR REPLACE FUNCTION myFunc(prm_MyParam integer)
  RETURNS numeric AS
$BODY$
BEGIN
  {...}

END;$BODY$
  LANGUAGE plpgsql STABLE;

Answer 2

使用子查询：

SELECT
    "Sum_one",
    "Sum_two",
    ("Sum_one" + "Sum_two") AS "Sum_three"
FROM (
    SELECT sum_one("A"."id") AS "Sum_one", sum_two("A"."id") AS "Sum_two" FROM A
)

PostgreSQL：在一个查询中多次调用同一个函数的最佳方法？

2 个答案: