u013628902的博客

题目要求：Given a Weather table, write a SQL query to find all dates' Ids with higher temperature compared to its previous (yesterday's) dates. 解答：关于时间的Mysql的函数： 1、TO_DAYS(date):给定一个日期data，返回从年份0开始的天数 2

题目要求：Write a SQL query to delete all duplicate email entries in a table named Person, keeping only unique emails based on its smallest Id. 解答： # Write your MySQL query statement below DELETE p1

题目要求：Suppose that a website contains two tables, the Customers table and the Orders table. Write a SQL query to find all customers who never order anything. 解答：1) LEFT JOIN 左联结： SELECT Name AS Custo

题目要求：Write a SQL query to find all duplicate emails in a table named Person. 解答：比较顺的思路就是用GROUP BY、HAVING ；但是还可以用DISTINCT 联表查询的方法。 1) SELECT Email FROM Person GROUP BY Email HAVING COUNT(*) >= 22) 摘

1、题目要求：Given the Employee table, write a SQL query that finds out employees who earn more than their managers. For the above table, Joe is the only employee who earns more than his manager.

1、题目要求（175、combine two tables）： 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 peopl

1、SQL语句的语法顺序为 SELECT[DISTINCT]   、FROM   、WHERE   、GROUP BY   、 HAVING     、UNION   、ORDER BY 2、FROM语句 FROM a,b  这句FROM语句的输出是一张联合报，联合了表a和表b，这个联合表里的数据是a*b，即a和b的笛卡尔积。 FROM输出的结果被WHERE语句筛选后要经过GROUP BY语

解答： 1）使用IF  UPDATE Salary SET sex = IF(sex='m','f','m') 或者使用 CASE WHEN... THEN ...ELSE...END 要注意语法问题 UPDATE Salary SET sex = (CASE WHEN sex='m' THEN 'f' ELSE 'm' END)

题目要求： There is a table courses with columns: student and class Please list out all classes which have more than or equal to 5 students. 解答：COUNT与 DISTINCT组合使用，满足The students should not be count