如何确定upsert是否是PostgreSQL 9.5+ UPSERT的更新？ [英] How to find out if an upsert was an update with PostgreSQL 9.5+ UPSERT?

问题描述

如插入，是否在PostgreSQL中进行重复更新？

是否可以使用信息将其最终更新为INSERT或执行INSERT来执行UPSERT以下可写CTE习惯用语：

It is possible to perform an UPSERT with the information whether it ended up as an UPDATE or an INSERT with the following Writable CTEs idiom:

WITH
    update_cte AS (
        UPDATE t SET v = $1 WHERE id = $2 RETURNING 'updated'::text status
    ),
    insert_cte AS (
        INSERT INTO t(id, v) SELECT $2, $1 WHERE NOT EXISTS
            (SELECT 1 FROM update_cte) RETURNING 'inserted'::text status
    )
 (SELECT status FROM update_cte) UNION (SELECT status FROM insert_cte)

此查询将返回 updated或 inserted，或者可能（很少）由于违反约束而失败，如 https://dba.stackexchange.com/questions/78510/why-is-cte-open-to-lost-updates

This query will return either "updated" or "inserted", or may (rarely) fail with a constraint violation in as described in https://dba.stackexchange.com/questions/78510/why-is-cte-open-to-lost-updates

可以使用PostgreSQL 9.5+新的 UPSERT语法实现类似的功能，并受益于其优化并避免了可能的约束冲突吗？

Can something similar be achieved using PostgreSQL 9.5+ new "UPSERT" syntax, benefiting from its optimization and avoiding the possible constraint violation?

推荐答案

我相信 xmax :: text :: int> 0 是最简单的把戏：

I believe xmax::text::int > 0 would be the easiest trick:

so=# DROP TABLE IF EXISTS tab;
NOTICE:  table "tab" does not exist, skipping
DROP TABLE
so=# CREATE TABLE tab(id INT PRIMARY KEY, col text);
CREATE TABLE
so=# INSERT INTO tab(id, col) VALUES (1,'a'), (2, 'b');
INSERT 0 2
so=# INSERT INTO tab(id, col)
VALUES (3, 'c'), (4, 'd'), (1,'aaaa')
ON CONFLICT (id) DO UPDATE SET col = EXCLUDED.col
returning *,case when xmax::text::int > 0 then 'updated' else 'inserted' end,ctid;
 id | col  |   case   | ctid
----+------+----------+-------
  3 | c    | inserted | (0,3)
  4 | d    | inserted | (0,4)
  1 | aaaa | updated  | (0,5)
(3 rows)

INSERT 0 3
so=# INSERT INTO tab(id, col)
VALUES (3, 'c'), (4, 'd'), (1,'aaaa')
ON CONFLICT (id) DO UPDATE SET col = EXCLUDED.col
returning *,case when xmax::text::int > 0 then 'updated' else 'inserted' end,ctid;
 id | col  |  case   | ctid
----+------+---------+-------
  3 | c    | updated | (0,6)
  4 | d    | updated | (0,7)
  1 | aaaa | updated | (0,8)
(3 rows)

INSERT 0 3

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