任務一:
創建一個新的數據庫:
create database DataWhale;
use DataWhale;
項目一:
創建一個新表email
create table email(
id int not null primary key,
Email varchar(255)
);
插入數據:
insert into email(id, email) values(1,'[email protected]'),(2,'[email protected]'),(3, '[email protected]');
查詢重複的email字典的內容
select email from (select email as email, count(*) as count from email group by email having count > 1) as dup_email;
輸出結果:
項目二:
創建數據表:
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
);
插入數據:
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);
如果一個國家的面積超過300萬平方公里,或者(人口超過2500萬並且gdp超過2000萬),那麼這個國家就是大國家。
編寫一個SQL查詢,輸出表中所有大國家的名稱、人口和麪積。
select name, population, area from world
where world.area > 3000000 or (population>25000000 and gdp>20000000);
輸出結果: