在写SQL解决业务问题遇到的一种情况

原表：

如下为数据库的两张表，表1为员工表；表2为员工奖金表。请根据各小题的输出结果，写出各小题的sql语句，请均用一句SQL语句实现。

建表语句：

-- create database employee;
-- use employee;
create table Employee(Employee_id int,
                      First_name varchar(50),
                      Last_name varchar(50),
                      Salary int,
                      Joining_date datetime,
                      Department varchar(50));
create table Incentive(Employee_id int,
                      Incentive_date datetime,
                      Incentive_amount int); 
alter table employee modify Joining_date varchar(50);
alter table Incentive modify Incentive_date varchar(50);
insert into employee values(1,'John','Abraham',1000000,'1-Jan-13','Banking');
insert into employee values(2,'Michael','Clarke',800000,'1-Jan-13','Insurance');
insert into employee values(3,'Roy','Thomas',700000,'1-Feb-13','Banking');
insert into employee values(4,'Tom','Jose',600000,'1-Feb-13','Insurance');
insert into employee values(5,'Jerry','Pinto',650000,'1-Feb-13','Insurance');
insert into employee values(6,'Philip','Mathew',750000,'1-Jan-13','Services');
insert into employee values(7,'Mark','King',650000,'1-Jan-13','Services');
insert into employee values(8,'Andrew','Lee',600000,'1-Feb-13','Insurance');

insert into incentive values(1,'1-Jan-13',5000);
insert into incentive values(2,'1-Jan-13',3000);
insert into incentive values(3,'1-Feb-13',4000);
insert into incentive values(1,'1-Jan-13',4500);
insert into incentive values(2,'1-Feb-13',3500);

-- 值得我学习！！！

1.输出第一个名字（First_name）包含’o’的所有雇员信息，并按薪资降序排列

输出结果如下：

SELECT * 
FROM Employee  
WHERE First_name  LIKE '%o%'
ORDER BY Salary DESC

2.输出每月的总支出工资大于1500000的部门和对应的支出，按降序排序。
输出结果如下：

SELECT 
Department AS dept_name,
SUM(salary) AS tatol_salary 
FROM Employee 
GROUP BY Department 
HAVING tatol_salary>1500000 
ORDER BY tatol_salary DESC

3.输出有奖金(Incentive)和没奖金的人数。
输出结果如下：

图1：

图2：

图3：

附正确代码：

-- 方法1：
-- 20200405
SELECT
sum(有无发奖金) AS 有奖金,
(COUNT(c.Employee_id) - sum(有无发奖金)) as 无奖金
FROM
(
SELECT
DISTINCT a.Employee_id  ,b.Employee_id I_Emp,
CASE
	WHEN b.Employee_id IS NULL THEN 0 ELSE 1 END AS `有无发奖金` 
FROM employee a
LEFT JOIN incentive b ON a.Employee_id = b.Employee_id)c

-- 使用中文给字段命名时，注意不要使用中文引号；最好的做法是不写引号，或者写入英文文引号

-- 方法2 ---也别有一番韵味(尤其是特意给两个字段重命名)
select sum(case when m.iid is not null then 1 else 0 end) as '有奖金', 
sum(case when m.iid is null then 1 else 0 end) as '无奖金'
from 
(select distinct e.employee_id as eid,
 -- e.First_name, 
i.employee_id as iid 
from employee e 
left join incentive i 
on e.employee_id = i.employee_id) m;

来自aishujuxueyuan月考题

学而实习之，不亦说乎！
还是要多锻炼一下自己独手写代码的能力；锻炼自己的思维逻辑性和逻辑连贯性，不能出错；