指向重复约束值的 Upsert 错误（On Conflict Do Update）

Question

当我尝试在 FROM 语句中使用多个源时，我在 Postgres 9.5 中遇到了 ON CONFLICT DO UPDATE 的问题。

工作代码示例：

    INSERT INTO new.bookmonographs  (citavi_id, abstract, createdon, edition, title, year)
SELECT "ID", "Abstract", "CreatedOn"::timestamp, "Edition", "Title", "Year"
FROM old."Reference"
WHERE old."Reference"."ReferenceType" = 'Book'
    AND old."Reference"."Year" IS NOT NULL
    AND old."Reference"."Title" IS NOT NULL
ON CONFLICT (citavi_id) DO UPDATE 
    SET (abstract, createdon, edition, title, year) = (excluded.abstract, excluded.createdon, excluded.edition, excluded.title, excluded.year)
; 

错误代码：

    INSERT INTO new.bookmonographs  (citavi_id, abstract, createdon, edition, title, year)
SELECT "ID", "Abstract", "CreatedOn"::timestamp, "Edition", "Title", "Year"
FROM old."Reference", old."ReferenceAuthor"
WHERE old."Reference"."ReferenceType" = 'Book'
    AND old."Reference"."Year" IS NOT NULL
    AND old."Reference"."Title" IS NOT NULL
    AND old."ReferenceAuthor"."ReferenceID" = old."Reference"."ID"
    --Year, Title and Author must be present in the data, otherwise the entry is deemed useless, hence won't be included
ON CONFLICT (citavi_id) DO UPDATE 
    SET (abstract, createdon, edition, title, year) = (excluded.abstract, excluded.createdon, excluded.edition, excluded.title, excluded.year)
; 

我在 FROM 语句和另一个 WHERE 语句中添加了一个额外的源，以确保只有具有标题、年份和作者的条目被插入到新数据库中。 （如果 old."Reference"."ID" 存在于 old."ReferenceAuthor" 为 "ReferenceID"，则存在作者。）即使没有附加的 WHERE 语句，查询也是错误的。我在 SELECT 中指定的列仅存在于 old."Reference" 中，而不存在于 old."ReferenceAuthor" 中。 目前old."ReferenceAuthor" 和old."Reference" 没有唯一约束，专着的唯一约束是：

CONSTRAINT bookmonographs_pk PRIMARY KEY (bookmonographsid),
CONSTRAINT bookmonographs_bookseries FOREIGN KEY (bookseriesid)
      REFERENCES new.bookseries (bookseriesid) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT bookmonographs_citaviid_unique UNIQUE (citavi_id)

PSQL 抛出的错误：

错误：ON CONFLICT DO UPDATE 命令不能再次影响行 提示：确保在同一命令中建议插入的行没有重复的约束值。 ********** 错误**********

错误：ON CONFLICT DO UPDATE 命令不能再次影响行 SQL 状态：21000 提示：确保在同一命令中建议插入的行没有重复的约束值。

我不知道出了什么问题，也不知道为什么提示指向重复的约束值。

Answer 1

postgres' docs（ctrl + f："Cardinality violation" errors in detail，因为没有直接链接）对此问题有很好的解释。

引用文档：

引发“基数违规”错误的想法是确保任何一行受到影响的每条语句不超过一次。在 SQL 标准讨论 SQL MERGE 的词典中，SQL 语句是“确定性的”。用户应该确信一行不会受到多次影响 - 如果不是这种情况，则无法预测多次受影响的行的最终值是什么。

为了重放他们更简单的示例，在表 upsert 上，以下查询无法正常工作，因为我们无法可靠地知道 select val from upsert where key = 1 是否等于 'Foo' 或 'Bar'：

 INSERT INTO upsert(key, val)
   VALUES(1, 'Foo'), (1, 'Bar')
   ON CONFLICT (key) UPDATE SET val = EXCLUDED.val;
 ERROR:  21000: ON CONFLICT UPDATE command could not lock/update self-inserted tuple
 HINT:  Ensure that no rows proposed for insertion within the same command have duplicate constrained values.

Answer 2

问题是由于某些条目显然有多个作者这一事实引起的。因此，您编写的选择查询中的内部联接将为同一条目返回多行，INSERT ... ON CONFLICT 不喜欢这样。由于您只使用ReferenceAuthor 表进行过滤，因此您可以简单地重写查询，以便它使用该表仅通过对相关子查询执行exists 来过滤没有任何作者的条目。方法如下：

INSERT INTO new.bookmonographs  (citavi_id, abstract, createdon, edition, title, year)
SELECT "ID", "Abstract", "CreatedOn"::timestamp, "Edition", "Title", "Year"
FROM old."Reference"
WHERE old."Reference"."ReferenceType" = 'Book'
    AND old."Reference"."Year" IS NOT NULL
    AND old."Reference"."Title" IS NOT NULL
    AND exists(SELECT FROM old."ReferenceAuthor" WHERE old."ReferenceAuthor"."ReferenceID" = old."Reference"."ID")
    --Year, Title and Author must be present in the data, otherwise the entry is deemed useless, hence won't be included
ON CONFLICT (citavi_id) DO UPDATE 
    SET (abstract, createdon, edition, title, year) = (excluded.abstract, excluded.createdon, excluded.edition, excluded.title, excluded.year)
; 

Answer 3

使用显式INNER JOIN 将两个源表连接在一起：

INSERT INTO new.bookmonographs  (citavi_id, abstract, createdon, edition, title, year)
SELECT "ID", "Abstract", "CreatedOn"::timestamp, "Edition", "Title", "Year"
FROM old."Reference"
INNER JOIN old."ReferenceAuthor"                                       -- explicit join
    ON old."ReferenceAuthor"."ReferenceID" = old."Reference"."ID"      -- ON condition
WHERE old."Reference"."ReferenceType" = 'Book' AND
      old."Reference"."Year" IS NOT NULL       AND
      old."Reference"."Title" IS NOT NULL
ON CONFLICT (citavi_id) DO UPDATE 
SET (abstract, createdon, edition, title, year) =
    (excluded.abstract, excluded.createdon, excluded.edition, excluded.title,
     excluded.year)