本文记录个人刷题记录

推荐两个刷题网站：

地址：https://leetcode.com/

另外一个地址：http://www.lintcode.com/

1.Write a SQL query to get the second highest salary from the Employee table.

题目地址：https://leetcode.com/problems/second-highest-salary/

+----+--------+

| Id | Salary |

+----+--------+

| 1  | 100    |

| 2  | 200    |

| 3  | 300    |

+----+--------+

For example, given the above Employee table, the second highest salary is 200.
If there is no second highest salary, then the query should return null.

解:

先算出所有员工中最高的工资，然后在从非最高工资中的记录，取最大的一个，就是第二高工资了

select max(Salary) as 'SecondHighestSalary'

from Employee where Salary<(select max(Salary) from Employee)

2.Given an array of integers, return indices of
the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

地址:https://leetcode.com/problems/two-sum/

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

解：

两层遍历，外层遍历是负责遍历每个元素，内层遍历是用于把当前外层循环去取出的数与除它之外的元素相加，看是否等于目标数值，如果等于，就返回当前两个元素的索引，如果都没有命中，就返回空数组

public class Solution {

    public int[] twoSum(int[] nums, int target) {

         for(int i=0 ;i<nums.length;i++){

           for(int j=i+1;j<nums.length;j++)

               if (nums[i] + nums[j] == target) {

                   return new int[]{

                       i,j

                   };

               }

       }

      return new int[]{};

    }

}

3.Combine Two Tables

Table: Person

+-------------+---------+

| Column Name | Type    |

+-------------+---------+

| PersonId    | int     |

| FirstName   | varchar |

| LastName    | varchar |

+-------------+---------+

PersonId is the primary key column for this table.

Table: Address

+-------------+---------+

| Column Name | Type    |

+-------------+---------+

| AddressId   | int     |

| PersonId    | int     |

| City        | varchar |

| State       | varchar |

+-------------+---------+

AddressId is the primary key column for this table.

Write a SQL query for a report that provides the following information for each person in the Person table, regardless if there is an
address for each of those people:

FirstName, LastName, City, State

解:

两个表通过PersonId关联查询即可，但是因为需要有所有Person表记录，所以这里要用leftjoin

SELECT pes.firstName as 'FirstName',

pes.LastName as 'LastName',

adr.City as 'City',

adr.State as 'State'

FROM Person pes

LEFT JOIN Address adr

on pes.personid = adr.personid;

巴特西

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