今天项目BOSS提了个sql语句需求，我听得稀里糊涂，没办法，一步步讨论、实践，最终搞定。
先上建表语句：
1 /* 2 Navicat MySQL Data Transfer 3 4 Source Server : localhost_3306 5 Source Server Version : 50623 6 Source Host : localhost:3306 7 Source Database : demo 8 9 Target Server Type : MYSQL 10 Target Server Version : 50623 11 File Encoding : 65001 12 13 Date: 2015-08-16 00:02:22 14 */ 15 16 SET FOREIGN_KEY_CHECKS=0; 17 18 -- ---------------------------- 19 -- Table structure for t_info 20 -- ---------------------------- 21 DROP TABLE IF EXISTS `t_info`; 22 CREATE TABLE `t_info` ( 23 `id` int(11) NOT NULL AUTO_INCREMENT, 24 `name` varchar(24) DEFAULT NULL, 25 `number` int(11) DEFAULT NULL, 26 PRIMARY KEY (`id`) 27 ) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=utf8; 28 29 -- ---------------------------- 30 -- Records of t_info 31 -- ---------------------------- 32 INSERT INTO `t_info` VALUES ('1', 'a', '18'); 33 INSERT INTO `t_info` VALUES ('2', 'b', '18'); 34 INSERT INTO `t_info` VALUES ('3', 'a', '17'); 35 INSERT INTO `t_info` VALUES ('4', 'a', '19'); 36 INSERT INTO `t_info` VALUES ('5', 'a', '20'); 37 INSERT INTO `t_info` VALUES ('6', 'b', '30'); 38 INSERT INTO `t_info` VALUES ('7', 'b', '31'); 39 INSERT INTO `t_info` VALUES ('8', 'b', '32'); 40 INSERT INTO `t_info` VALUES ('9', 'a', '25'); 41 INSERT INTO `t_info` VALUES ('10', 'b', '26');