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Update MySQL学习笔记.md
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mysql/MySQL学习笔记.md

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@@ -722,7 +722,7 @@ SELECT NO FROM course WHERE t_no = ( SELECT NO FROM teacher WHERE NAME = '张旭
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```mysql
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SELECT * FROM score WHERE c_no = (
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SELECT no FROM course WHERE t_no = (
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SELECT no FROM course WHERE t_no = (
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SELECT no FROM teacher WHERE NAME = '张旭'
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)
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);
@@ -1570,7 +1570,7 @@ SELECT * FROM user;
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>
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> `@@AUTOCOMMIT = 0` 时,使用 `COMMIT` 命令提交事务。
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>
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> 3. **事务回滚**
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> 3. **事务回滚**
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>
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> `@@AUTOCOMMIT = 0` 时,使用 `ROLLBACK` 命令回滚事务。
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### 事务的隔离性
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**事务的隔离性可分为四种 ( 性能从低到高 )**
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**事务的隔离性可分为四种 ( 性能从低到高 )**
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1. **READ UNCOMMITTED ( 读取未提交 ) **
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1. **READ UNCOMMITTED ( 读取未提交 )**
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如果有多个事务,那么任意事务都可以看见其他事务的**未提交数据**
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2. **READ COMMITTED ( 读取已提交 ) **
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2. **READ COMMITTED ( 读取已提交 )**
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只能读取到其他事务**已经提交的数据**
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3. **REPEATABLE READ ( 可被重复读 ) **
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3. **REPEATABLE READ ( 可被重复读 )**
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如果有多个连接都开启了事务,那么事务之间不能共享数据记录,否则只能共享已提交的记录。
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