I have a table named Worker Send Times and in there are two fields named start and end (both are timestamp):

if I have all records I want to get the difference in hours from start and end time and the total count how many times he worked so I have to do at first differnce in hours and then calculate all diference in hours with all records. My current query is this:

    SELECT
        
        wst.id,
        wst.start_time as start,
        wst.end_time as end,
  
        l.name,
  
        FROM workers_send_times wst
  
        INNER JOIN workers_plan wp
        ON wp.id = wst.workers_plan_id
  
        LEFT JOIN location_orders lo
        ON lo.id = wp.location_orders_id
  
        LEFT JOIN location l 
        ON l.id = lo.location_id
  
        WHERE wst.user_id = $2
        AND extract(MONTH FROM start) = $3 AND extract(YEAR FROM end) = $6
  
        ORDER BY wst.id, wst.send_start_at
  

in the query I only want to show the records from a given month and year. But how can I get the difference in hours and total all counts ?