EXPLAIN select c_custkey, c_name, sum(l_extendedprice * (1 - l_discount)) as revenue, c_acctbal, n_name, c_address, c_phone, c_comment from customer, orders, lineitem, nation where c_custkey = o_custkey and l_orderkey = o_orderkey and o_orderdate >= date '1994-11-01' and o_orderdate < date '1994-11-01' + interval '3 months' and l_returnflag = 'R' and c_nationkey = n_nationkey group by c_custkey, c_name, c_acctbal, c_phone, n_name, c_address, c_comment order by revenue desc LIMIT 20;
                  plan                   
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                  sort                  
                                        
                 groupby                
                                        
                  join                  
                  hash                  
                                        
             join              tablescan
             hash              lineitem 
                                        
 tablescan       join                   
 nation          indexnl                
                                        
           tablescan tablescan          
           orders    customer           
(15 rows)