概述每一种字符串类型的特性；给出一些简单的示例并且概括如何在需要的时候将一种字符串类型转换成其它的类型。
-An overview of each of the string types of properties gives examples of some simple and summed up how to, when necessary, will be a string type conversion into other types.
SHOW FULL COLUMNS FROM `jrk_downrecords` [ RunTime:0.002051s ]
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:0.085601s ]
SHOW FULL COLUMNS FROM `jrk_tagrecords` [ RunTime:0.003254s ]
SELECT * FROM `jrk_tagrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 20 [ RunTime:0.003278s ]
SHOW FULL COLUMNS FROM `jrk_member` [ RunTime:0.003421s ]
SELECT `id`,`username`,`userhead`,`usertime` FROM `jrk_member` WHERE `status` = 1 ORDER BY `usertime` DESC LIMIT 10 [ RunTime:0.006310s ]
SHOW FULL COLUMNS FROM `jrk_searchrecords` [ RunTime:0.002943s ]
SELECT * FROM `jrk_searchrecords` WHERE `status` = 1 ORDER BY `num` DESC LIMIT 5 [ RunTime:0.003325s ]
SELECT aid,title,count(aid) as c FROM `jrk_downrecords` GROUP BY `aid` ORDER BY `c` DESC LIMIT 10 [ RunTime:0.015904s ]
SHOW FULL COLUMNS FROM `jrk_articles` [ RunTime:0.002761s ]
UPDATE `jrk_articles` SET `hits` = 1 WHERE `id` = 106503 [ RunTime:0.001312s ]
