Postgresql 从INSERT或SELECT获取id

我有一个函数，它在

city

表中插入一行，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

标记我需要这样东西的地方：

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，并且我没有从中获取

id\u city

，我希望执行第二个查询以选择现有的

id\u city

---

我怎样才能做到这一点呢？

为什么不这样修改你的函数呢

将现有的

id\u city

插入

id\u city1

。如果一个不存在，它将是

NULL

。然后，如果

INSERT

为

NULL

，则可以执行

INSERT

，并分配新的

id\u city1

。最后返回

id\u 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;

---

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Postgres9.5或更高版本，因为您没有声明它

• 使用新的快速插入解决方案

  INSERT。。关于冲突…

  
  详细说明：
• 为此，您需要

  唯一的
  限制
  城市名称
  

• 关于

  联合所有。。。限制1

  ：
• 可以通过使用数据修改CTE的单个SQL命令来实现。这是最不容易受到锁争用或其他并发问题影响的。即使没有并发访问，它也是最短、最快的

• 该函数可以是更简单的SQL函数。（但plpgsql也没有错或坏。）

• 不要滥用的别名将名称附加到参数。手册中明确不鼓励这样做。使用正确的参数名
  最好仅将其用于覆盖预定名称的目的

---

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，当行存在时，不增加主键号（在这种情况下为id\u city）？
存在竞争条件。当并发事务同时提交时，即使第一次选择没有找到行，也可能会遇到唯一的冲突。有一些更快的解决方案没有显示此问题。错误：没有唯一或排除约束与启动期间的冲突规范SQL状态：42P10上下文：SQL函数“insert_city”匹配