MERGE INTO 
    rlarp.walk w
USING 
    ( SELECT $1 ship_cust, $2 bucket, $3 notes) as i ON
        i.ship_cust = w.ship_cust
WHEN MATCHED THEN UPDATE SET 
    bucket = i.bucket
    ,notes = i.notes
WHEN NOT MATCHED THEN 
    INSERT (ship_cust, bucket, notes)
    VALUES (i.ship_cust, i.bucket, i.notes )