CREATE INDEX i_o_orderdate ON orders (o_orderdate);

CREATE INDEX i_o_custkey ON orders (o_custkey);

MariaDB [dbt3]> explain select * from orders,customer where o_custkey=c_custkey order by o_orderdate limit 10;

+------+-------------+----------+--------+---------------+---------------+---------+-----------------------+------+-------------+

| id   | select_type | table    | type   | possible_keys | key           | key_len | ref                   | rows | Extra       |

+------+-------------+----------+--------+---------------+---------------+---------+-----------------------+------+-------------+

|    1 | SIMPLE      | orders   | index  | i_o_custkey   | i_o_orderdate | 4       | NULL                  | 10   | Using where |

|    1 | SIMPLE      | customer | eq_ref | PRIMARY       | PRIMARY       | 4       | dbt3.orders.o_custkey | 1    |             |

+------+-------------+----------+--------+---------------+---------------+---------+-----------------------+------+-------------+

MariaDB [dbt3]> explain select * from orders,customer where o_custkey=c_custkey order by c_acctbal limit 10; 

+------+-------------+----------+-------+---------------+-------------+---------+-------------------------+------+-------+

| id   | select_type | table    | type  | possible_keys | key         | key_len | ref                     | rows | Extra |

+------+-------------+----------+-------+---------------+-------------+---------+-------------------------+------+-------+

|    1 | SIMPLE      | customer | index | PRIMARY       | c_acctbal   | 9       | NULL                    | 1    |       |

|    1 | SIMPLE      | orders   | ref   | i_o_custkey   | i_o_custkey | 5       | dbt3.customer.c_custkey | 15   |       |

+------+-------------+----------+-------+---------------+-------------+---------+-------------------------+------+-------+

 MariaDB [dbt3]> select * from information_schema.optimizer_trace\G

 *************************** 1. row ***************************

-                            QUERY: explain select * from orders,customer where o_custkey=c_custkey order by o_orderdate limit 10

+                            QUERY: explain select * from orders,customer where o_custkey=c_custkey order by c_acctbal limit 10

                             TRACE: {

   "steps": [

     {

@@ -18,7 +17,7 @@

         "select_id": 1,

         "steps": [

           {

-            "expanded_query": ...

+            "expanded_query": ...

           } 

         ] 

       } 

@@ -177,15 +176,15 @@

           },

           {

             "attaching_conditions_to_tables": {

-              "original_condition": "customer.c_custkey = orders.o_custkey",

+              "original_condition": "orders.o_custkey = customer.c_custkey",

               "attached_conditions_computation": [],

               "attached_conditions_summary": [

                 {

-                  "table": "orders",

-                  "attached": "orders.o_custkey is not null"

+                  "table": "customer",

+                  "attached": null

                 },