select * from departmentsDEPARTMENT_ID DEPARTMENT_NAME MANAGER_ID LOCATION_ID
10         Administration 200         1700
20         Marketing 201         1800
50         Shipping 124         1500
60         IT 103 1400
80         Sales 149 2500
90         Executive 100         1700
110         Accounting 205         1700
190         Contracting         1700
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SELECT department_id, department_name
FROM departments d
WHERE NOT EXISTS (SELECT 'X'
                  FROM   employees
                  WHERE  department_id
                         = d.department_id);
DEPARTMENT_ID DEPARTMENT_NAME
190 Contracting
为什么会有190显示,190明明有匹配啊,求解。