如何查看upsert是否是PostgreSQL 9.5+ UPSERT的更新？

Question

可写CTE被认为是9.5之前的UPSERT的解决方案,如插入,PostgreSQL中的重复更新中所述？

可以执行带有以下信息的UPSERT,无论它是以UPDATE还是INSERT与以下可写CTE惯用语:

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"已更新"或"已插入",或者可能(很少)因违反约束而失败,如https://dba.stackexchange.com/questions/78510/why-is-cte-open-to中所述-lost-更新

使用PostgreSQL 9.5+新的"UPSERT"语法可以实现类似的功能,从优化中获益并避免可能的约束违规吗？

Answer 1

我认为xmax::text::int > 0这是最简单的伎俩:

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

Answer 2

从图形@ lad2025的答案,结果可能滥用实现设置和自定义选项与相关功能在WHERE子句来获得所需的副作用.

CREATE TABLE t(id INT PRIMARY KEY, v TEXT);

INSERT INTO t (id, v)
    SELECT $1, $2
    WHERE 'inserted' = set_config('upsert.action', 'inserted', true)
    ON CONFLICT (id) DO UPDATE
        SET v = EXCLUDED.v
        WHERE 'updated' = set_config('upsert.action', 'updated', true)
RETURNING current_setting('upsert.action') AS "upsert.action";

第三个参数set_config是is_local:true表示设置将在交易结束时消失.更准确地说,current_setting('upsert.action')将返回NULL(并且不会抛出错误)直到会话结束.

Answer 3

在SQL Server MERGE 语句$action中返回字符串'INSERT', 'UPDATE', or 'DELETE'.

因为Postgresql我找不到类似的功能/变量RETURNING.

解决方法的一种方法是向is_updated表中添加列:

DROP TABLE IF EXISTS tab;

CREATE TABLE tab(id INT PRIMARY KEY, col VARCHAR(100),
                 is_updated BOOLEAN DEFAULT false);
INSERT INTO tab(id, col) VALUES (1,'a'), (2, 'b');


-- main query
INSERT INTO tab(id, col)
VALUES (3, 'c'), (4, 'd'), (1,'aaaa')
ON CONFLICT (id) DO UPDATE SET col = EXCLUDED.col, is_updated = true
RETURNING id,col,
          CASE WHEN is_updated THEN 'UPDATED' ELSE 'INSERTED' END AS action;

Rextester演示

输出:

????????????????????????
? id ? col  ?  action  ?
????????????????????????
?  3 ? c    ? INSERTED ?
?  4 ? d    ? INSERTED ?
?  1 ? aaaa ? UPDATED  ?
????????????????????????