实现二叉树的基本功能，包括前序遍历，中序遍历，后序遍历，层次遍历-To achieve the basic functions of a binary tree, including the pre-order traversal, inorder traversal, postorder, level traversal
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.004005s ]
SELECT `a`.`aid`,`a`.`title`,`a`.`create_time`,`m`.`username` FROM `jrk_downrecords` `a` INNER JOIN `jrk_member` `m` ON `a`.`uid`=`m`.`id` WHERE `a`.`status` = 1 GROUP BY `a`.`aid` ORDER BY `a`.`create_time` DESC LIMIT 10 [ RunTime:0.128071s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.001010s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.001118s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.000967s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.003168s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.000912s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.003936s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.019814s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.010172s ]
UPDATE `jrk_articles` SET `hits` = 2 WHERE `id` = 180376 [ RunTime:0.013838s ]
