〈数据结构〉习题集1.19 1.20 4.17答案，经多次修改而成，比答案册的还要简单易懂。- Exercise Set 1.19 1.20 4.17 answer, several revisions, the book also answers simple and understandable.
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.000992s ]
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:0.135238s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.000947s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.001123s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.001021s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.003211s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.000950s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.004364s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.015857s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.001169s ]
UPDATE `jrk_articles` SET `hits` = 2 WHERE `id` = 72007 [ RunTime:0.015806s ]
