Question

我有下表：

create table foobar
(
    account_id  bigint    not null,
    timestamp   timestamp not null,
    balance_one numeric   not null,
    balance_two numeric   not null,

    primary key (timestamp, account_id),
);

目前，我使用以下语句一次将数千条记录插入到该表中：

insert into foobar(account_id, timestamp, balance_one, balance_two)
VALUES (?, ?, ?, ?), (?, ?, ?, ?), ETC...
on conflict DO NOTHING;

我想在插入语句中添加一个约束，如果 new.balance_one == old.balance_one AND new.balance_two == old.balance_two 停止插入新记录其中 old = 最近的（时间戳）记录，其中 account_id = new.account_id。

我该怎么做？插入性能也是一个问题。

Answer 1

也许您应该看看 ON INSERT 触发器。您可以创建一个函数：

CREATE OR REPLACE FUNCTION check_insert() RETURNS TRIGGER AS $$
DECLARE rec foobar;
BEGIN
  SELECT balance_one,balance_two FROM foobar INTO rec.balance_one,rec.balance_two
  WHERE account_id = NEW.account_id
  ORDER BY timestamp DESC LIMIT 1;    
  IF rec.balance_one = NEW.balance_one AND
     rec.balance_two = NEW.balance_two THEN
    RETURN OLD; -- this will silently ignore the insert for the current record
  ELSE
    RETURN NEW;
 END IF;
END; $$ LANGUAGE plpgsql;

...并将其附加到您的桌子上

CREATE TRIGGER trg_check_balances BEFORE INSERT ON foobar
FOR EACH ROW EXECUTE PROCEDURE check_insert();

演示：db<>fiddle

注意：如果您尝试在同一事务中插入具有相同 acount_id 的两条记录，则此方法将失败，因为事务中的所有记录都将获得相同的 {{1}并且您的主键将被违反。

Answer 2

INSERT INTO foobar(account_id, timestamp, balance_one, balance_two)
WITH oldies AS (
   SELECT DISTINCT ON (account_id)
        account_id, timestamp, balance_one, balance_two
   FROM foobar
   ORDER BY account_Id, timestamp DESC
)
SELECT n.*
FROM (VALUES (?, ?, ?, ?), (?, ?, ?, ?), ...)
  AS n(account_id, timestamp, balance_one, balance_two)
LEFT JOIN oldies o
ON n.account_id = o.account_id
WHERE o.account_id IS NULL OR NOT (
    n.balance_one = o.balance_one
    AND
    n.balance_two = o.balance_two
  )
ON CONFLICT DO NOTHING;

Postgresql - 如何仅在满足特定条件时插入

2 个答案: