01 · What is it?
A transaction is a group of database operations treated as one complete unit.
The database commits the unit when every required operation succeeds. If an operation fails, the transaction can roll back the earlier changes.
MODULE 05 · DATABASE & SQL
Transaction
A transaction groups multiple database operations into one logical unit so they can succeed or fail together.
02 · Think of it like…
Think of moving money between two bank accounts.
One account must be debited and the other must be credited. You do not want only one side to change, so both steps belong to the same all-or-nothing unit.
Debit Account ARemove the money.
→
Credit Account BAdd the money.
→
CommitKeep both changes.
03 · What does it do?
A transaction helps a database:
Group operationsKeep related changes together.
Commit changesMake successful work permanent.
Roll back changesUndo partial work after failure.
Protect consistencyPrevent incomplete business results.
04 · Where is it used?
Transactions are useful whenever one business action changes more than one piece of data.
Bank transfersDebit one account and credit another.
Order checkoutCreate an order and reserve inventory.
PaymentsRecord payment and update order status.
ReservationsBook a resource and mark it unavailable.
Account changesUpdate related user records together.
Batch updatesApply a set of changes as one unit.
05 · Example
Transfer 100 from one account to another
BEGIN;
UPDATE accounts
SET balance = balance - 100
WHERE id = 1;
UPDATE accounts
SET balance = balance + 100
WHERE id = 2;
COMMIT;If either update fails, the application can roll back the transaction so the transfer does not leave the accounts in an incomplete state.
06 · How it connects
Request→
Backend→
Begin Transaction→
SQL Operations→
Commit or Rollback→
Response
The backend decides which operations belong together and reports whether the unit completed successfully.
07 · Do Not Confuse
Transaction
A unit that groups related database operations.
Query
One request to read or change database data.
Commit
Make a successful transaction permanent.
Rollback
Undo the changes made by a transaction.
08 · Topic Glossary
| ENGLISH TERM | 中文 | SIMPLE ENGLISH | 中文小白理解 |
|---|---|---|---|
| Transaction | 事务 | A group of database operations treated as one logical unit. | 把多条数据库操作当成一个整体来执行。 |
| Atomicity | 原子性 | All operations in a transaction succeed together or fail together. | 要么全部成功，要么全部失败，不能只完成一半。 |
| Commit | 提交 | Make the changes in a successful transaction permanent. | 确认这次事务成功，并把改动正式保存下来。 |
| Rollback | 回滚 | Undo changes made during a transaction. | 出错时撤销这次事务已经做过的改动。 |
| Consistency | 一致性 | Keep data valid according to the database rules. | 事务前后都要遵守数据规则，不能留下不合法的数据。 |
| Isolation | 隔离性 | Control how concurrent transactions see each other’s changes. | 多个事务同时运行时，控制它们互相看到哪些改动。 |
| BEGIN | 开始事务 | Start a transaction block. | 告诉数据库，接下来的操作属于同一个事务。 |
| SQL | 结构化查询语言 | A language used to work with relational database data. | 用来查询和修改关系型数据库数据的语言。 |
09 · What to Remember
A transaction groups related database operations into one logical unit.
Commit makes the whole unit permanent; rollback undoes its changes after failure.
Use transactions when a business action must not leave partial data behind.