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Update SQL 练习.md

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调整代码块语言，补充参考资料。
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CyC2018
2026-10-28 03:18:55 +08:00
parent 322915d361
commit 44a57adc7e
1 changed files with 38 additions and 32 deletions
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notes/SQL 练习.md
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@@ -16,6 +16,7 @@
* [178. Rank Scores](#178-rank-scores)
* [180. Consecutive Numbers](#180-consecutive-numbers)
* [626. Exchange Seats](#626-exchange-seats)
* [参考资料](#参考资料)
<!-- GFM-TOC -->
@@ -25,7 +26,7 @@ https://leetcode.com/problems/big-countries/description/
### Description
```html
```text
+-----------------+------------+------------+--------------+---------------+
| name | continent | area | population | gdp |
+-----------------+------------+------------+--------------+---------------+
@@ -39,7 +40,7 @@ https://leetcode.com/problems/big-countries/description/
查找面积超过 3,000,000 或者人口数超过 25,000,000 的国家。
```html
```text
+--------------+-------------+--------------+
| name | population | area |
+--------------+-------------+--------------+
@@ -85,7 +86,7 @@ https://leetcode.com/problems/swap-salary/description/
### Description
```html
```text
| id | name | sex | salary |
|----|------|-----|--------|
| 1 | A | m | 2500 |
@@ -96,7 +97,7 @@ https://leetcode.com/problems/swap-salary/description/
只用一个 SQL 查询，将 sex 字段反转。
```html
```text
| id | name | sex | salary |
|----|------|-----|--------|
| 1 | A | f | 2500 |
@@ -145,7 +146,7 @@ https://leetcode.com/problems/not-boring-movies/description/
### Description
```html
```text
+---------+-----------+--------------+-----------+
| id | movie | description | rating |
+---------+-----------+--------------+-----------+
@@ -159,7 +160,7 @@ https://leetcode.com/problems/not-boring-movies/description/
查找 id 为奇数，并且 description 不是 boring 的电影，按 rating 降序。
```html
```text
+---------+-----------+--------------+-----------+
| id | movie | description | rating |
+---------+-----------+--------------+-----------+
@@ -204,7 +205,7 @@ https://leetcode.com/problems/classes-more-than-5-students/description/
### Description
```html
```text
+---------+------------+
| student | class |
+---------+------------+
@@ -222,7 +223,7 @@ https://leetcode.com/problems/classes-more-than-5-students/description/
查找有五名及以上 student 的 class。
```html
```text
+---------+
| class |
+---------+
@@ -273,7 +274,7 @@ https://leetcode.com/problems/duplicate-emails/description/
邮件地址表：
```html
```text
+----+---------+
| Id | Email |
+----+---------+
@@ -285,7 +286,7 @@ https://leetcode.com/problems/duplicate-emails/description/
查找重复的邮件地址：
```html
```text
+---------+
| Email |
+---------+
@@ -331,7 +332,7 @@ https://leetcode.com/problems/delete-duplicate-emails/description/
邮件地址表：
```html
```text
+----+---------+
| Id | Email |
+----+---------+
@@ -343,7 +344,7 @@ https://leetcode.com/problems/delete-duplicate-emails/description/
删除重复的邮件地址：
```html
```text
+----+------------------+
| Id | Email |
+----+------------------+
@@ -413,7 +414,7 @@ https://leetcode.com/problems/combine-two-tables/description/
Person 表：
```html
```text
+-------------+---------+
| Column Name | Type |
+-------------+---------+
@@ -426,7 +427,7 @@ PersonId is the primary key column for this table.
Address 表：
```html
```text
+-------------+---------+
| Column Name | Type |
+-------------+---------+
@@ -483,7 +484,7 @@ https://leetcode.com/problems/employees-earning-more-than-their-managers/descrip
Employee 表：
```html
```text
+----+-------+--------+-----------+
| Id | Name | Salary | ManagerId |
+----+-------+--------+-----------+
@@ -531,7 +532,7 @@ https://leetcode.com/problems/customers-who-never-order/description/
Customers 表：
```html
```text
+----+-------+
| Id | Name |
+----+-------+
@@ -544,7 +545,7 @@ Customers 表：
Orders 表：
```html
```text
+----+------------+
| Id | CustomerId |
+----+------------+
@@ -555,7 +556,7 @@ Orders 表：
查找没有订单的顾客信息：
```html
```text
+-----------+
| Customers |
+-----------+
@@ -624,7 +625,7 @@ https://leetcode.com/problems/department-highest-salary/description/
Employee 表：
```html
```text
+----+-------+--------+--------------+
| Id | Name | Salary | DepartmentId |
+----+-------+--------+--------------+
@@ -637,7 +638,7 @@ Employee 表：
Department 表：
```html
```text
+----+----------+
| Id | Name |
+----+----------+
@@ -648,7 +649,7 @@ Department 表：
查找一个 Department 中收入最高者的信息：
```html
```text
+------------+----------+--------+
| Department | Employee | Salary |
+------------+----------+--------+
@@ -706,7 +707,7 @@ https://leetcode.com/problems/second-highest-salary/description/
### Description
```html
```text
+----+--------+
| Id | Salary |
+----+--------+
@@ -718,7 +719,7 @@ https://leetcode.com/problems/second-highest-salary/description/
查找工资第二高的员工。
```html
```text
+---------------------+
| SecondHighestSalary |
+---------------------+
@@ -791,7 +792,7 @@ https://leetcode.com/problems/rank-scores/description/
得分表：
```html
```text
+----+-------+
| Id | Score |
+----+-------+
@@ -806,7 +807,7 @@ https://leetcode.com/problems/rank-scores/description/
将得分排序，并统计排名。
```html
```text
+-------+------+
| Score | Rank |
+-------+------+
@@ -851,7 +852,7 @@ ORDER BY
|1| 4.1 |2| 4.2|
|1| 4.1 |3| 4.3|
可以看到每个 S1.score 都有对应好几条记录，我们再进行分组，并统计每个分组的数量作为 'Rank'
可以看到每个 S1.score 都有对应好几条记录，再进行分组，并统计每个分组的数量作为 'Rank'
```sql
SELECT
@@ -887,7 +888,7 @@ ORDER BY
| 4.2 | 2 |
| 4.1 | 3 |
而我们希望的结果为：
而希望的结果为：
| score | Rank |
| :---: | :--: |
@@ -907,7 +908,7 @@ ORDER BY
| 1 | 4.1 | 2 | 4.2 |
| 1 | 4.1 | 1 | 4.1 |
我们想要的结果是，把分数相同的放在同一个排名，并且相同分数只占一个位置，例如上面的分数，Id=2 和 Id=3 的记录都有相同的分数，并且最高，他们并列第一。而 Id=1 的记录应该排第二名，而不是第三名。所以在进行 COUNT 计数统计时，我们需要使用 COUNT( DISTINCT S2.score ) 从而只统计一次相同的分数。
想要的结果是，把分数相同的放在同一个排名，并且相同分数只占一个位置，例如上面的分数，Id=2 和 Id=3 的记录都有相同的分数，并且最高，他们并列第一。而 Id=1 的记录应该排第二名，而不是第三名。所以在进行 COUNT 计数统计时，需要使用 COUNT( DISTINCT S2.score ) 从而只统计一次相同的分数。
```sql
SELECT
@@ -948,7 +949,7 @@ https://leetcode.com/problems/consecutive-numbers/description/
数字表：
```html
```text
+----+-----+
| Id | Num |
+----+-----+
@@ -964,7 +965,7 @@ https://leetcode.com/problems/consecutive-numbers/description/
查找连续出现三次的数字。
```html
```text
+-----------------+
| ConsecutiveNums |
+-----------------+
@@ -1013,7 +1014,7 @@ https://leetcode.com/problems/exchange-seats/description/
seat 表存储着座位对应的学生。
```html
```text
+---------+---------+
| id | student |
+---------+---------+
@@ -1027,7 +1028,7 @@ seat 表存储着座位对应的学生。
要求交换相邻座位的两个学生，如果最后一个座位是奇数，那么不交换这个座位上的学生。
```html
```text
+---------+---------+
| id | student |
+---------+---------+
@@ -1091,3 +1092,8 @@ VALUES
( '4', 'Green' ),
( '5', 'Jeames' );
```
## 参考资料
- [LeetCode 数据库题库](https://leetcode.com/problemset/database/)
- [MySQL 8.0 Reference Manual](https://dev.mysql.com/doc/refman/8.0/en/)