Question

我在postgresql中有一个事务，我执行以下命令：

SELECT "amount", "accountId" from "transactions" where "id" = "123"
DELETE from "transactions" where "id" = "123"
UPDATE "accounts" set "balance" = "balance" - amountFetchedInCommand1 where "id" = accountFetchedInCommand1

现在我需要确保在命令1和2之间从transactions获取的行没有被修改（特别是其amount和accountId字段。

我是否可以使用SELECT FOR UPDATE语句来锁定在命令1处获取的行，即使我不会更新行但只删除它？

否则，确保此操作始终正确运行的最佳方法是什么？

（transactions.accountId是与account.id ON DELETE CASCADE相关联的外键

Answer 1

您可以在一个声明中执行第2步和第3步：

with deleted as (
   DELETE from transactions 
   where id = 123
   return amount, "accountId"
)
UPDATE accounts 
   set balance = accounts.balance - d.amount 
from deleted d
where accounts.id = d."accountId";

Answer 2

使用开始; //代码提交;

或开始交易[参数] //代码Comit;

更多文档：http://www.postgresql.org/docs/9.1/static/sql-start-transaction.html

删除前PostgreSQL锁定行？

2 个答案: