इसे आज़माएं:
SELECT
b.calendar_id,
a.employee_id,
a.weekday
FROM
(SELECT
`weekday`,
MAX(employee_id) AS employee_id
FROM
calendar
WHERE employee_id = 1
OR employee_id IS NULL
GROUP BY `weekday`) a
LEFT JOIN calendar b
ON a.weekday = b.weekday
AND a.employee_id = b.employee_id ;
किसी भी स्पष्टीकरण के मामले में मुझे बताएं।