Database: Database practice

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1. database software installation and configuration

server host installation mariadb server software and remote login database;
installation:

yum install mariadb-server -y

Start the service:

systemctl start mariadb
systemctl enable mariadb

Configure remote login:

mysql_secure_installation	# 设置本地密码
systemctl stop firewalld.service		# 关火墙
systemctl disable firewalld.service
mysql -uroot -p		   # 进入数据库
grant all privileges on *.* to root@'172.25.254.68' 
identified by 'westos';	
# 允许172.25.254.68使用root用户登陆数据库，密码为westos

test:

2. N-th high salary: Get here claim 2 high salary salary

answer:

select Salary from Employee order by Salary asc limit 1,1;

3. Score sorting

Write a SQL query to achieve the score rankings. If the two scores are the same, in accordance id descending
order.

A:

select Id, Score from Score order by Score desc, Id asc;

4. Find duplicate e-mail

answer:

select Email from Email group by Email having count(*)> 1;

5. income employees than managers

answer:

select a.Name from StaffSalare as a,StaffSalare as b 
where a.ManageId = b.Id and a.Salary > b.Salary;

6. Never order customers

answer:

select Name as Customers from Customers 
where not Customers.Id in 
(select Customers from Orders);