SQL Query on Employee Assignment Details

Hello,

Please i need a query to return employee details like name, department, grade, step, date of first appointment and date of present appointment. I currently have one a query i have built but it is returning more than one row for the same employee. I want to be able to link it grade and assignment so it can return just one row for that employee. Below is the one i am using.

How can i improve on this query to achieve that or if you have one that can do that, please share.

SELECT

A.EMPLOYEE_NUMBER StaffNumber,

  A.LAST_NAME AS LAST_NAME,