Question

我有这个函数在city表中插入一行而没有重复。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标志着我需要这样的地方：

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而我没有从中获取id_city，我想执行第二个查询以选择现有的id_city。

我该怎么做？

Answer 1

您的功能可以简化一些。更重要的是，您可以修复内置竞争条件：

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;

重点

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：
- 的 Is SELECT or INSERT in a function prone to race conditions?

您需要在UNIQUE上使用 name_city 约束。

关于UNION ALL ... LIMIT 1：

Way to try multiple SELECTs till a result is available?

使用数据修改CTE的单个SQL命令可以实现。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。

该函数可以是更简单的 SQL函数。（但是plpgsql也没有错或坏。）

请勿滥用 ~~ALIAS FOR~~ 将名称附加到参数。这在手册中明确表示不鼓励。使用正确的参数名称。 The manual:

最好只将其用于覆盖预定名称。

Answer 2

为什么不改变你的功能？：

将现有id_city插入id_city1。如果不存在，则为NULL。然后，您可以INSERT执行NULL并分配新的id_city1。最后返回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 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编号（在这种情况下为id_city）？

从INSERT或SELECT

3 个答案:

重点