Re: N-to-N Model: Table Size vs Complexity

[Rick James]

CREATE TABLE `db`.`friends` (
   `a` varchar(10) NOT NULL COMMENT 'SELECT a FROM friends WHERE b = person UNION SELECT b FROM friends WHERE a = person',
   `b` varchar(10) NOT NULL,
   PRIMARY KEY `friend` (a, b),
   KEY (b, a)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC COMMENT='mapping relationships between people';

VARCHAR -- unless all your friends have exactly 10 letters?
InnoDB works better with a PRIMARY KEY.

These changes are only a start -- When you get some more fields and some more SELECTs, you may need more hints.