Json111的博客

在员工工资表中返回第二高的记录，如果没有则返回null。使用limit offsetSELECT (SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 1) AS SecondHighestS...

select Email from( select Email, count(Email) as num from Person group by Email) as statisticwhere num > 1;group by 和 havingselect Emailfrom Persongroup by Emailhaving count(Emai...