从 INSERT 或 SELECT 获取 id

Question

我有这个函数可以在 city table 中插入一行而不重复。它returns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 ;
country1 ALIAS FOR ;
province1 ALIAS FOR ;
region1 ALIAS FOR ;
cap1 ALIAS FOR ;
nationality1 ALIAS FOR ;
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得到 id_city，我想执行第二个查询 select 一个现有的 id_city .

我该怎么做？

Answer 1

为什么不这样改变你的函数呢？:

将现有的 id_city 插入 id_city1。如果一个不存在，它将是 NULL。如果它是 NULL，然后您可以执行 INSERT 并分配新的 id_city1。最后 return id_city1.

SELECT id_city INTO id_city1 FROM city WHERE name_city = name_city1;

IF id_city1 IS NULL THEN

    INSERT INTO city (name_city, country, province, region, cap, nationality) 
    VALUES (name_city1, country1, province1, region1, cap1, nationality1)
    RETURNING id_city INTO id_city1;

END IF;

RETURN id_city1;

Answer 2

你的函数可以再简化一些。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

假设你运行 Postgres 9.5 或更高版本，因为你没有声明它。
使用新的更快的 UPSERT 解决方案INSERT .. ON CONFLICT ...
详细解释：
- Is SELECT or INSERT in a function prone to race conditions?
为此，您需要 UNIQUE name_city 约束。
关于UNION ALL ... LIMIT 1:
- Way to try multiple SELECTs till a result is available?
可以通过使用数据修改 CTE 的单个 SQL 命令来实现。这最不容易受到锁争用或其他并发问题的影响。即使没有并发访问也是最短最快的。
函数可以是更简单的SQL函数。（但是 plpgsql 也不错。）
不要滥用 ~~ALIAS FOR~~ 为参数附加名称。手册中明确不鼓励这样做。使用正确的参数名称。 The manual:

It's best to use it only for the purpose of overriding predetermined names.

Answer 3

这是plpgsql版本

CREATE OR REPLACE FUNCTION public.insert_city(name_city1   varchar
                                        , country1     varchar
                                        , province1    varchar
                                        , region1      varchar
                                        , zip1         varchar
                                        , nationality1 varchar,
                                        OUT id_city1 int)
  AS
 $func$
 BEGIN
    INSERT INTO city
        (name_city , country , province , region , zip , nationality ) 
    VALUES(name_city1, country1, province1, region1, zip1, nationality1)
    ON CONFLICT (name_city,zip) DO UPDATE
    SET    name_city = NULL WHERE FALSE  -- never executed, but locks the row!
    RETURNING id_city
    INTO id_city1;

    IF NOT FOUND THEN
        SELECT id_city
        FROM city
        WHERE name_city = name_city1
        INTO id_city1;
    END IF;
  END  $func$  LANGUAGE plpgsql;

有一种方法可以在行存在时不增加 primary_key 数字（在这种情况下为 id_city）？

从 INSERT 或 SELECT 获取 id

Get id from INSERT or SELECT

postgresql

plpgsql

insert-select

要点