MYSQL - GROUP BY

NOT LIKE ORACLE /MSSQL ,

MYSQL CAN SELECT MULTI COLUMN WHEN USING GROUP BY

SELECT DISTINCT(employee_id) , department_id 
FROM
(SELECT employee_id , department_id 
FROM
Employee 
GROUP BY
employee_id
HAVING
COUNT(1) <2
UNION ALL
SELECT employee_id ,department_id 
FROM
Employee
WHERE 
primary_flag = 'Y') as u

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