Sql query error

hello to all, I have a problem with my sql query which displays null at the level of the 'description' field

here are my 4 tables

tbl_prod (id_prod,description)    tbl_demand( id_dmd,qty_request,qty_served,date_dmd)    tbl_employee(id_emp,name, unit) and intermediate table   tbl_concern(id_prod,id_dmd

I would like my request to show me the tbl_employee.name, tbl_employee.unit, tbl_demand.qty_request, tbl_demand.qty_served, tbl_demand.date_dmd, tbl_prod.description but unfortunately at the level of the chanp description c null which appears, here is my request : 

SELECT description;qty_request,qty_dmd,date_dmd,name,unit from tbl_prod 
right join tbl_concern on tbl_prod.id_prod=tbl_concer.id_prod
right join tbl_demand on tbl_demand.id_dmd=concerne.id_dmd
left join tbl_employee on tbl_employee.id_emp=tbl_dmd.id_emp

can someone help me to see a little more clearly 

thank you