leecode 数据库题

codes/leetcode/classes-more-than-5-students.sql

@@ -0,0 +1,30 @@
+--    有一个courses 表 ，有: student (学生) 和 class (课程)。
+--
+--    请列出所有超过或等于5名学生的课。
+--
+--    例如,表:
+--
+--    +---------+------------+
+--    | student | class      |
+--    +---------+------------+
+--    | A       | Math       |
+--    | B       | English    |
+--    | C       | Math       |
+--    | D       | Biology    |
+--    | E       | Math       |
+--    | F       | Computer   |
+--    | G       | Math       |
+--    | H       | Math       |
+--    | I       | Math       |
+--    +---------+------------+
+--    应该输出:
+--
+--    +---------+
+--    | class   |
+--    +---------+
+--    | Math    |
+--    +---------+
+--    Note:
+--    学生在每个课中不应被重复计算。
+
+SELECT class FROM courses GROUP BY class HAVING COUNT(DISTINCT student)>4;

codes/leetcode/combine-two-tables.sql

@@ -0,0 +1,33 @@
+--    表1: Person
+--
+--    +-------------+---------+
+--    | 列名         | 类型     |
+--    +-------------+---------+
+--    | PersonId    | int     |
+--    | FirstName   | varchar |
+--    | LastName    | varchar |
+--    +-------------+---------+
+--    PersonId 是上表主键
+--    表2: Address
+--
+--    +-------------+---------+
+--    | 列名         | 类型    |
+--    +-------------+---------+
+--    | AddressId   | int     |
+--    | PersonId    | int     |
+--    | City        | varchar |
+--    | State       | varchar |
+--    +-------------+---------+
+--    AddressId 是上表主键
+--
+--
+--    编写一个 SQL 查询，满足条件：无论 person 是否有地址信息，都需要基于上述两表提供 person 的以下信息：
+--
+--
+--
+--    FirstName, LastName, City, State
+
+SELECT Person.FirstName, Person.LastName, Address.City, Address.State
+FROM Person
+LEFT JOIN Address
+ON Person.PersonId = Address.PersonId;

codes/leetcode/customers-who-never-order.sql

@@ -0,0 +1,36 @@
+--    某网站包含两个表，Customers 表和 Orders 表。编写一个 SQL 查询，找出所有从不订购任何东西的客户。
+--
+--    Customers 表：
+--
+--    +----+-------+
+--    | Id | Name  |
+--    +----+-------+
+--    | 1  | Joe   |
+--    | 2  | Henry |
+--    | 3  | Sam   |
+--    | 4  | Max   |
+--    +----+-------+
+--    Orders 表：
+--
+--    +----+------------+
+--    | Id | CustomerId |
+--    +----+------------+
+--    | 1  | 3          |
+--    | 2  | 1          |
+--    +----+------------+
+--    例如给定上述表格，你的查询应返回：
+--
+--    +-----------+
+--    | Customers |
+--    +-----------+
+--    | Henry     |
+--    | Max       |
+--    +-----------+
+
+SELECT Name AS Customers FROM Customers c
+WHERE c.Id NOT IN (SELECT DISTINCT CustomerId FROM Orders);
+
+SELECT Name AS Customers
+FROM Customers
+INNER JOIN Orders
+ON Customers.Id != Orders.CustomerId;

codes/leetcode/employees-earning-more-than-their-managers.sql

@@ -0,0 +1,33 @@
+--    Employee 表包含所有员工，他们的经理也属于员工。每个员工都有一个 Id，此外还有一列对应员工的经理的 Id。
+--
+--    +----+-------+--------+-----------+
+--    | Id | Name  | Salary | ManagerId |
+--    +----+-------+--------+-----------+
+--    | 1  | Joe   | 70000  | 3         |
+--    | 2  | Henry | 80000  | 4         |
+--    | 3  | Sam   | 60000  | NULL      |
+--    | 4  | Max   | 90000  | NULL      |
+--    +----+-------+--------+-----------+
+--    给定 Employee 表，编写一个 SQL 查询，该查询可以获取收入超过他们经理的员工的姓名。
+--    在上面的表格中，Joe 是唯一一个收入超过他的经理的员工。
+--
+--    +----------+
+--    | Employee |
+--    +----------+
+--    | Joe      |
+--    +----------+
+
+-- 以下 3 种解法，由上至下，处理速度越来越慢：
+-- 第 1 种查询
+SELECT e1.Name AS Employee
+FROM Employee e1
+INNER JOIN Employee e2
+ON e1.ManagerId = e2.Id AND e1.Salary > e2.Salary;
+
+-- 第 2 种解法
+SELECT e1.Name AS Employee FROM Employee e1, Employee  e2
+WHERE e1.ManagerId = e2.Id AND e1.Salary > e2.Salary;
+
+-- 第 3 种查询
+SELECT e1.Name AS Employee FROM Employee e1 WHERE
+e1.Salary > (SELECT e2.Salary FROM Employee e2 WHERE e1.ManagerId = e2.Id);

codes/leetcode/rising-temperature.sql

@@ -0,0 +1,22 @@
+--    给定一个 Weather 表，编写一个 SQL 查询，来查找与之前（昨天的）日期相比温度更高的所有日期的 Id。
+--
+--    +---------+------------------+------------------+
+--    | Id(INT) | RecordDate(DATE) | Temperature(INT) |
+--    +---------+------------------+------------------+
+--    |       1 |       2015-01-01 |               10 |
+--    |       2 |       2015-01-02 |               25 |
+--    |       3 |       2015-01-03 |               20 |
+--    |       4 |       2015-01-04 |               30 |
+--    +---------+------------------+------------------+
+--    例如，根据上述给定的 Weather 表格，返回如下 Id:
+--
+--    +----+
+--    | Id |
+--    +----+
+--    |  2 |
+--    |  4 |
+--    +----+
+
+SELECT w1.Id FROM Weather w1, Weather w2
+WHERE w1.RecordDate = DATE_ADD(w2.RecordDate,interval 1 DAY )
+AND w1.Temperature > w2.Temperature;

codes/leetcode/second-highest-salary.sql

@@ -0,0 +1,21 @@
+--    编写一个 SQL 查询，获取 Employee 表中第二高的薪水（Salary） 。
+--
+--    +----+--------+
+--    | Id | Salary |
+--    +----+--------+
+--    | 1  | 100    |
+--    | 2  | 200    |
+--    | 3  | 300    |
+--    +----+--------+
+--    例如上述 Employee 表，SQL查询应该返回 200 作为第二高的薪水。如果不存在第二高的薪水，那么查询应返回 null。
+--
+--    +---------------------+
+--    | SecondHighestSalary |
+--    +---------------------+
+--    | 200                 |
+--    +---------------------+
+
+
+SELECT (SELECT DISTINCT salary FROM Employee
+ORDER BY salary DESC LIMIT 1,1)
+AS SecondHighestSalary;