mysql方法来源于:http://www.cnblogs.com/jjcc/p/5896588.html ###在网上看到一篇,非常赞的方法### 比如说要获取班级的前3名,mysql就可以用GROUP_CONCAT + GROUP BY + substring_index实现. 考试表 DROP TABLE IF EXISTS `test`;CREATE TABLE `test` (`id` int(11) DEFAULT NULL,`name` varchar(20) DEFAULT N
一.NSClassFromString是NSObjCRuntime.h的方法 FOUNDATION_EXPORT Class __nullable NSClassFromString(NSString *aClassName); Description:Obtains a class by name.The name of a class.Parameters:aClassName The name of a classReturns:The class object named by aCla