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@ -465,7 +465,7 @@ Java 内存模型定义了 8 种操作来完成工作内存与主内存之间的
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Java 内存模型允许虚拟机将没有被 volatile 修饰的 64 位数据的读写操作划分为两次 32 位的操作来进行,即虚拟机可以不保证 64 位数据类型的 load、store、read 和 write 这 4 个操作的原子性。但是目前各种平台下的商用虚拟机几乎都选择把 64 位数据的读写操作作为原子操作来对待。
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Java 内存模型允许虚拟机将没有被 volatile 修饰的 64 位数据的读写操作划分为两次 32 位的操作来进行,即虚拟机可以不保证 64 位数据类型的 load、store、read 和 write 这 4 个操作的原子性。但是目前各种平台下的商用虚拟机几乎都选择把 64 位数据的读写操作作为原子操作来对待。
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**AtomicInteger、AtomicLong、AtomicReference** 等特殊的原子性变量类提供了下面形式的原子性条件更新语句,使得比较和更新这两个操作能够不可分割地执行。
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AtomicInteger、AtomicLong、AtomicReference 等特殊的原子性变量类提供了下面形式的原子性条件更新语句,使得比较和更新这两个操作能够不可分割地执行。
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```java
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```java
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boolean compareAndSet(expectedValue, updateValue);
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boolean compareAndSet(expectedValue, updateValue);
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@ -407,7 +407,7 @@ ORDER BY cust_name;
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内连接又称等值连接,使用 INNER JOIN 关键字。
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内连接又称等值连接,使用 INNER JOIN 关键字。
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```
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```sql
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select a, b, c
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select a, b, c
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from A inner join B
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from A inner join B
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on A.key = B.key
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on A.key = B.key
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@ -415,7 +415,7 @@ on A.key = B.key
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可以不明确使用 INNER JOIN,而使用普通查询并在 WHERE 中将两个表中要连接的列用等值方法连接起来。
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可以不明确使用 INNER JOIN,而使用普通查询并在 WHERE 中将两个表中要连接的列用等值方法连接起来。
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```
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```sql
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select a, b, c
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select a, b, c
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from A, B
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from A, B
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where A.key = B.key
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where A.key = B.key
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@ -431,7 +431,7 @@ where A.key = B.key
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**子查询版本**
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**子查询版本**
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```
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```sql
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select name
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select name
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from employee
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from employee
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where department = (
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where department = (
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@ -442,7 +442,7 @@ where department = (
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**自连接版本**
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**自连接版本**
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```
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```sql
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select name
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select name
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from employee as e1, employee as e2
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from employee as e1, employee as e2
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where e1.department = e2.department
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where e1.department = e2.department
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@ -457,7 +457,7 @@ where e1.department = e2.department
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内连接和自然连接的区别:内连接提供连接的列,而自然连接自动连接所有同名列。
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内连接和自然连接的区别:内连接提供连接的列,而自然连接自动连接所有同名列。
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```
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```sql
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select *
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select *
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from employee natural join department;
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from employee natural join department;
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```
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```
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@ -468,7 +468,7 @@ from employee natural join department;
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检索所有顾客的订单信息,包括还没有订单信息的顾客。
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检索所有顾客的订单信息,包括还没有订单信息的顾客。
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```
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```sql
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select Customers.cust_id, Orders.order_num
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select Customers.cust_id, Orders.order_num
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from Customers left outer join Orders
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from Customers left outer join Orders
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on Customers.cust_id = Orders.curt_id;
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on Customers.cust_id = Orders.curt_id;
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@ -476,7 +476,7 @@ select Customers.cust_id, Orders.order_num
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如果需要统计顾客的订单数,使用聚集函数。
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如果需要统计顾客的订单数,使用聚集函数。
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```
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```sql
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select Customers.cust_id,
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select Customers.cust_id,
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COUNT(Orders.order_num) as num_ord
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COUNT(Orders.order_num) as num_ord
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from Customers left outer join Orders
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from Customers left outer join Orders
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