【原创】测试关联预载入对性能的提升效果
关联查询的预查询载入功能，主要解决了N+1次查询的问题，例如下面的查询如果有4个记录，会执行5次查询：
// 关联预载入之前$start_time = microtime();$list = Model\User::select([1,2,3,4]);foreach($list as $key=>$user){var_dump($user->profile);}$diff_time = microtime() – $start_time;var_dump($diff_time);
float0.047106
如果使用关联预查询功能，对于一对一关联来说，只有一次查询，对于一对多关联的话，就可以变成2次查询，有效提高性能。
// 关联预载入之后$start_time = microtime();$list = Model\User::with(‘profile’)->select([1,2,3,4]);foreach($list as $key=>$user){var_dump($user->profile);}$diff_time = microtime() – $start_time;var_dump($diff_time);
float0.030193
总结：预载入之后相对于预载入之前，查询速度上有显著提升，数据量越大，提升效果越明显！
查询记录如下：
// 5次查询分别为： SELECT * FROM `user` WHERE ( `id` IN (1,2,3,4) ) AND `user`.`delete_time` IS NULL; SELECT * FROM `profile` WHERE ( `user_id` = 1 ) AND `profile`.`delete_time` IS NULL LIMIT 1; SELECT * FROM `profile` WHERE ( `user_id` = 2 ) AND `profile`.`delete_time` IS NULL LIMIT 1; SELECT * FROM `profile` WHERE ( `user_id` = 3 ) AND `profile`.`delete_time` IS NULL LIMIT 1; SELECT * FROM `profile` WHERE ( `user_id` = 4 ) AND `profile`.`delete_time` IS NULL LIMIT 1; // 2次查询分别为： SELECT * FROM `user` WHERE ( `id` IN (1,2,3,4) ) AND `user`.`delete_time` IS NULL; SELECT * FROM `profile` WHERE ( `user_id` IN (1,2,3,4) ) AND `profile`.`delete_time` IS NULL;