我正在学习SQL，并在MySQL中创建了以下数据集:
Create table Departments (DepartmentID int primary key, Name text);
insert into Departments values
(1001,'SRO'),
(2001,'Drs'),
(3001,'Accounting');
Create table Employees
(
EmployeeID int not null,
DepartmentID int not null,
ManagerID int,
Name varchar(50) not null,
Salary int not null,
primary key(EmployeeID),
foreign key (DepartmentID)
references Departments(DepartmentID)
);
insert into Employees values
(68319,1001,NULL,'Kayling','6000.00'),
(66928,3001,68319,'Blaze','2750.00'),
(67832,1001,68319,'Clare','2550.00'),
(65646,2001,68319,'Jonas','2957.00'),
(67858,2001,65646,'Scarlet','3100.00'),
(69062,2001,65646,'Frank','3100.00'),
(63679,2001,69062,'Sandrine','900.00'),
(64989,3001,66928,'Adelyn','1700.00'),
(65271,3001,66928,'Wade','1350.00');
我想找出每个部门的最高工资，研究了我看到的许多文章，建议以这种形式运行MAX:
SELECT max(Salary),DepartmentID
FROM Employees
GROUP BY DepartmentID;
然而，根据答案here中描述的操作顺序，
FROM, including JOINs
WHERE
SELECT the row obtained by from and where in a temporary area for others
operation (and build the column alias)
DISTINCT
GROUP BY
HAVING
ORDER BY
LIMIT and OFFSET
return the final result
在GROUP BY之前调用MAX函数，这意味着在执行GROUP BY之前，MAX将在整个表中运行，根据我的理解，这应该导致出现单个最大值across the table，该值应该是6000.然而，情况并非如此，我确实看到的结果令人困惑，我想要的 struct 是正确的:
max(Salary) DepartmentID
6000 1001
3100 2001
2750 3001
不知何故，MAX函数在GROUP BY之后工作，但也在由于GROUP BY删除多个组行而丢失所有行之前工作.
如果我继续这样理解，就会给我带来更多的问题.
如果对SELECT执行GROUP BY操作before，则GROUP BY将删除每个DepartmentID的所有行，只保留一行randomly chosen，这意味着当SELECT中的MAX函数有机会运行时，它将只看到一个工资值，该值可以是任何值，而不是每个部门的最大值.
我错过了什么让我的理解变得复杂的地方？