MySQL - 在 select 内选择并使用 NOT EXISTS

Question

I have these tables:

WORKERS(Id integer PRIMARY KEY, Name text, Phone text, Age integer, Dapartment 
text)

Dapartments(Name text, Manger text)

And I want to get the name of an employee who has only one manager, I guess there are a total of 2 managers, and each employee can have 2 managers (at least 1).

I try to do:

SELECT Name, 
       Manger 
  FROM (SELECT * 
          FROM WORKERS 
               INNER JOIN Dapartments 
                  ON WORKERS.Dapartment = Dapartments.Name 
         WHERE Manger = 'manger1') 
 WHERE NOT EXSITS (SELECT * 
                     FROM WORKERS 
                         INNER JOIN Dapartments 
                            ON WORKERS.Dapartment = Dapartments.Name 
                    WHERE Manger = 'manger2');

And I get this error:

Error: near line 52: near "SELECT": syntax error

What is wrong here?

Thanks

Answer 1

You need an table alias name for the FROM( ) Table_name _alias ( in this sample T)

    SELECT T.Name, 
           T.Manger 
    FROM (
        SELECT * 
        FROM WORKERS 
        INNER JOIN Dapartments ON WORKERS.Dapartment = Dapartments.Name 
        WHERE Manger = 'manger1'
        )  T 
     WHERE NOT EXSITS (
        SELECT * 
        FROM WORKERS 
        INNER JOIN Dapartments ON WORKERS.Dapartment = Dapartments.Name 
        WHERE Manger = 'manger2'
        );

Answer 2

One way is below:

Select w.Name ,d.Manger 
    From Dapartments d
    Join Workers w
    On W.Dapartment = D.Name
Where w.id in (  
Select Id, --count(Dapartment) As Mangrs 
From WORKERS 
group by Id 
Having count(Dapartment)=1
           )

--- If only Worker Name is required then:

 Select t.Name As Single_Mgr_Worker 
From (
Select Name, count(Dapartment) As Mangrs 
From WORKERS 
group by Id 
Having count(Dapartment)=1
           ) t