Upsert error (On Conflict Do Update) pointing to duplicate constrained values

问题

I have a problem with ON CONFLICT DO UPDATE in Postgres 9.5 when I try to use more than one source in the FROM statement.

Example of working code:

    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)
;

Faulty code:

    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)
;

I added an additional source in the FROM statement and one more WHERE statement to make sure only entries that have a title, year and author are inserted into the new database. (If old."Reference"."ID" exists in old."ReferenceAuthor" as "ReferenceID", then an author exists.) Even without the additional WHERE statement the query is faulty. The columns I specified in SELECT are only present in old."Reference", not in old."ReferenceAuthor". Currently old."ReferenceAuthor" and old."Reference" don't have a UNIQUE CONSTRAINT,the uniqe constraints for bookmonographs are:

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)

The error PSQL throws:

ERROR: ON CONFLICT DO UPDATE command cannot affect row a second time HINT: Ensure that no rows proposed for insertion within the same command have duplicate constrained values. ********** Error **********

ERROR: ON CONFLICT DO UPDATE command cannot affect row a second time SQL state: 21000 Hint: Ensure that no rows proposed for insertion within the same command have duplicate constrained values.

I don't know what's wrong, or why the hint points to a duplicated constrained value.

回答1:

The problem is caused by the fact that apparently some entries have multiple authors. So the inner join in the select query that you wrote will return multiple rows for the same entry and INSERT ... ON CONFLICT doesn't like that. Since you only use the ReferenceAuthor table for filtering, you can simply rewrite the query so that it uses that table to only filter entries that don't have any author by doing an exists on a correlated subquery. Here's how:

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)
;

回答2:

Use an explicit INNER JOIN to join the two source tables together:

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)

来源：https://stackoverflow.com/questions/39767369/upsert-error-on-conflict-do-update-pointing-to-duplicate-constrained-values

标签

postgresql

upsert