我有这个函数,可以在 city
表中插入一行,而不重复。它返回插入行的 ID:
CREATE OR REPLACE FUNCTION public.insert_city(
character varying,
character varying,
character varying,
character varying,
character varying,
character varying)
RETURNS integer AS
$BODY$
DECLARE
name_city1 ALIAS FOR $1;
country1 ALIAS FOR $2;
province1 ALIAS FOR $3;
region1 ALIAS FOR $4;
cap1 ALIAS FOR $5;
nationality1 ALIAS FOR $6;
id_city1 integer;
BEGIN
INSERT INTO city (name_city, country, province, region, cap, nationality)
SELECT name_city1, country1, province1, region1, cap1, nationality1
WHERE NOT EXISTS (SELECT id_city FROM city WHERE name_city = name_city1)
RETURNING id_city INTO id_city1;
-- xxx
END;
$BODY$
LANGUAGE plpgsql VOLATILE;
xxx
标记了我需要这样的东西的地方:
IF is_number(id_city1) THEN
RETURN id_city1;
ELSE
RETURN query select id_city from city where name_city=name_city1;
END IF;
如果第一个查询没有插入新行并且我没有从中获得 id_city
,我想执行第二个查询以选择现有的 id_city
.
我该怎么做?
最佳答案
您的功能可以进一步简化。更重要的是,您可以修复内置的竞争条件:
CREATE OR REPLACE FUNCTION public.insert_city(name_city1 varchar
, country1 varchar
, province1 varchar
, region1 varchar
, cap1 varchar
, nationality1 varchar)
RETURNS integer AS
$func$
WITH ins AS (
INSERT INTO city
(name_city , country , province , region , cap , nationality )
VALUES(name_city1, country1, province1, region1, cap1, nationality1)
ON CONFLICT (name_city) DO UPDATE
SET name_city = NULL WHERE FALSE -- never executed, but locks the row!
RETURNING id_city
)
SELECT id_city FROM ins
UNION ALL
SELECT id_city FROM city WHERE name_city = name_city1 -- only executed if no INSERT
LIMIT 1;
$func$ LANGUAGE sql;
要点
假设您运行 Postgres 9.5 或更高版本,因为您没有声明它。
使用新的更快的 UPSERT 解决方案
INSERT .. ON CONFLICT ...
详细解释:为此,您需要
name_city
上的UNIQUE
约束。关于
UNION ALL ... LIMIT 1
:可以使用数据修改 CTE 通过单个 SQL 命令实现。这最不容易受到锁争用或其他并发问题的影响。即使没有并发访问,它也是最短和最快的。
该函数可以是一个更简单的SQL 函数。 (但 plpgsql 也没有错或坏。)
不要滥用
将名称附加到参数。手册中明确不鼓励这样做。使用正确的参数名称。 The manual:ALIAS FOR
It's best to use it only for the purpose of overriding predetermined names.
关于postgresql - 从 INSERT 或 SELECT 获取 id,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39779145/