175. Combine Two Tables
https://leetcode.com/problems/combine-two-tables/description/
SELECT FirstName, LastName, City, State
FROM Person AS p
LEFT JOIN Address as a
ON p.PersonId = a.PersonId
176. Second Highest Salary
https://leetcode.com/problems/second-highest-salary/description/
LIMIT a OFFSET b
取出第b+1条记录起的a条记录
SELECT Salary AS SecondHighestSalary
FROM Employee
ORDER BY Salary
LIMIT 1 OFFSET 1
SELECT max(Salary) AS SecondHighestSalary
FROM Employee
WHERE Salary < (SELECT max(Salary) FROM Employee)
