任务一:
创建一个新的数据库:
create database DataWhale;
use DataWhale;
项目一:
创建一个新表email
create table email(
id int not null primary key,
Email varchar(255)
);
插入数据:
insert into email(id, email) values(1,'[email protected]'),(2,'[email protected]'),(3, '[email protected]');
查询重复的email字典的内容
select email from (select email as email, count(*) as count from email group by email having count > 1) as dup_email;
输出结果:
项目二:
创建数据表:
CREATE TABLE World (
name VARCHAR(50) NOT NULL,
continent VARCHAR(50) NOT NULL,
area INT NOT NULL,
population INT NOT NULL,
gdp INT NOT NULL
);
插入数据:
INSERT INTO World
VALUES('Afghanistan','Asia',652230,25500100,20343000);
INSERT INTO World
VALUES('Albania','Europe',28748,2831741,12960000);
INSERT INTO World
VALUES('Algeria','Africa',2381741,37100000,188681000);
INSERT INTO World
VALUES('Andorra','Europe',468,78115,3712000);
INSERT INTO World
VALUES('Angola','Africa',1246700,20609294,100990000);
如果一个国家的面积超过300万平方公里,或者(人口超过2500万并且gdp超过2000万),那么这个国家就是大国家。
编写一个SQL查询,输出表中所有大国家的名称、人口和面积。
select name, population, area from world
where world.area > 3000000 or (population>25000000 and gdp>20000000);
输出结果: