在 PostgreSQL 中重复更新时插入? [英] Insert, on duplicate update in PostgreSQL?

问题描述

几个月前，我从 Stack Overflow 上的一个答案中了解到如何使用以下语法在 MySQL 中一次执行多个更新:

Several months ago I learned from an answer on Stack Overflow how to perform multiple updates at once in MySQL using the following syntax:

INSERT INTO table (id, field, field2) VALUES (1, A, X), (2, B, Y), (3, C, Z)
ON DUPLICATE KEY UPDATE field=VALUES(Col1), field2=VALUES(Col2);

我现在已经切换到 PostgreSQL，显然这不正确.它指的是所有正确的表，所以我认为这是使用不同关键字的问题，但我不确定 PostgreSQL 文档中的哪个位置.

I've now switched over to PostgreSQL and apparently this is not correct. It's referring to all the correct tables so I assume it's a matter of different keywords being used but I'm not sure where in the PostgreSQL documentation this is covered.

为了澄清，我想插入一些东西，如果它们已经存在，就更新它们.

To clarify, I want to insert several things and if they already exist to update them.

推荐答案

PostgreSQL 自 9.5 版起具有 UPSERT 语法，带有 ON CONFLICT 子句. 使用以下语法(类似于 MySQL)

PostgreSQL since version 9.5 has UPSERT syntax, with ON CONFLICT clause. with the following syntax (similar to MySQL)

INSERT INTO the_table (id, column_1, column_2) 
VALUES (1, 'A', 'X'), (2, 'B', 'Y'), (3, 'C', 'Z')
ON CONFLICT (id) DO UPDATE 
  SET column_1 = excluded.column_1, 
      column_2 = excluded.column_2;

<小时>

在 postgresql 的电子邮件组档案中搜索upsert"导致找到 在手册中做你可能想做的事的例子:

示例 38-2.UPDATE/INSERT 异常

此示例使用异常处理来执行 UPDATE 或 INSERT，视情况而定:

This example uses exception handling to perform either UPDATE or INSERT, as appropriate:

CREATE TABLE db (a INT PRIMARY KEY, b TEXT);

CREATE FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
    LOOP
        -- first try to update the key
        -- note that "a" must be unique
        UPDATE db SET b = data WHERE a = key;
        IF found THEN
            RETURN;
        END IF;
        -- not there, so try to insert the key
        -- if someone else inserts the same key concurrently,
        -- we could get a unique-key failure
        BEGIN
            INSERT INTO db(a,b) VALUES (key, data);
            RETURN;
        EXCEPTION WHEN unique_violation THEN
            -- do nothing, and loop to try the UPDATE again
        END;
    END LOOP;
END;
$$
LANGUAGE plpgsql;

SELECT merge_db(1, 'david');
SELECT merge_db(1, 'dennis');

<小时>

黑客邮件列表:

WITH foos AS (SELECT (UNNEST(%foo[])).*)
updated as (UPDATE foo SET foo.a = foos.a ... RETURNING foo.id)
INSERT INTO foo SELECT foos.* FROM foos LEFT JOIN updated USING(id)
WHERE updated.id IS NULL;

请参阅a_horse_with_no_name 的答案以获得更清晰的示例.

See a_horse_with_no_name's answer for a clearer example.

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