mysql - 如何根据先前的值更新列？

Question

我在这里阅读了很多答案，但无法适应我的需求。

我想在下面的表格中更新 BALANCE 列:

余额 = 旧余额 + 新金额

+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+
| ID | TRANSACTION_ID | BANK_ID | ACCOUNT_ID | CUSTOMER_ID | CREATED             | DESCRIPTION      | AMOUNT | CURRENCY | BALANCE |
+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+
|  1 | T1             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | 100.00 | GBP      |    NULL |
|  2 | T2             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | 125.00 | GBP      |    NULL |
|  3 | T3             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | -73.00 | GBP      |    NULL |
+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+

这是我想要的结果，如下所示: 我让它执行:

SET @balance:=0;
UPDATE TRANSACTIONS SET BALANCE = (@balance := @balance + AMOUNT) WHERE ID > 0;

插入新列后无法触发上面的语句吗？

+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+
| ID | TRANSACTION_ID | BANK_ID | ACCOUNT_ID | CUSTOMER_ID | CREATED             | DESCRIPTION      | AMOUNT | CURRENCY | BALANCE |
+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+
|  1 | T1             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | 100.00 | GBP      |  100.00 |
|  2 | T2             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | 125.00 | GBP      |  225.00 |
|  3 | T3             |       2 |          2 |           1 | 2018-04-22 00:00:00 | TRANSACTION TEST | -73.00 | GBP      |  152.00 |
+----+----------------+---------+------------+-------------+---------------------+------------------+--------+----------+---------+

我尝试使用触发器:

DELIMITER $$ 
CREATE TRIGGER updateBalance AFTER INSERT ON TRANSACTIONS 
FOR EACH ROW 
BEGIN
    SET NEW.BALANCE = BALANCE + NEW.AMOUNT;
END $$ 
DELIMITER ;

我得到了错误:

错误代码:1362。触发器后不允许更新新行

我是 SQL 和 MySQL 新手，我相信这是高级用户的常见任务。

Answer 1

不应具体化可以从其他(具体化)值计算得出的值，因为这可能会导致不一致。

将列全部删除。

ALTER TABLE transactions
            DROP balance;

并创建一个 View :

CREATE VIEW transactions_with_balance
AS
SELECT t1.*,
       (SELECT sum(t2.amount)
               FROM transactions t2
               WHERE t2.bank_id = t1.bank_id
                     AND t2.account_id = t1.account_id
                     AND t2.id <= t1.id) balance
       FROM transactions t1;

db<>fiddle

如果您使用的是 MySQL 版本 8 或更高版本，您还可以将子查询替换为窗口版本的 sum()

CREATE VIEW transactions_with_balance
AS
SELECT t1.*,
       sum(amount) OVER (PARTITION BY t1.bank_id,
                                      t1.account_id
                         ORDER BY t1.id) balance
       FROM transactions t1;

db<>fiddle

列customer_id在表中似乎也放错了位置，因为我认为有一个帐户表，其中帐户所属的客户存储在客户表的外键中。因此您可以通过 account_id 获取客户。