積集合。使ったことありません。
SELECT
e.EmployeeName AS 氏名
, s.SaleDate AS 日付
FROM
Sales AS s
JOIN
Employees AS e
ON s.EmployeeID = e.EmployeeID
INTERSECT
SELECT
e.EmployeeName AS 氏名
, s.PayDate AS 日付
FROM
Salary AS s
JOIN
Employees AS e
ON s.EmployeeID = e.EmployeeID
;