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)