Re: MySQL not using indexes

[Rick James]

SELECT  *
    FROM  territory_borders_finished, territories_finished
    where  tb_game_number=378664
      and  te_game_number=378664
      and  tb_border = te_code
    ORDER BY  tb_territory;

The "standard" way to specify that query is

SELECT  *
    FROM  territory_borders_finished, territories_finished
    where  tb_game_number=te_game_number  -- I changed this
      and  te_game_number=378664
      and  tb_border = te_code
    ORDER BY  tb_territory;

See if that works out better. Also, add
INDEX(tb_game_number, tb_border, tb_territory)
It may help even more.

By saying tb_game_number=te_game_number instead of tb_game_number=(constant), MySQL realizes that you are tying the tables together.