标签:分组 sdn ODB splay null rds style end opened
参考链接:https://blog.csdn.net/rainyspring4540/article/details/50231435
t_vehicle表有如下数据:
sql初始化语句如下:
-- ---------------------------- -- Table structure for t_vehicle -- ---------------------------- DROP TABLE IF EXISTS `t_vehicle`; CREATE TABLE `t_vehicle` ( `Vehicle_no` varchar(20) DEFAULT NULL, `Type` varchar(20) DEFAULT NULL ) ENGINE=InnoDB DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of t_vehicle -- ---------------------------- INSERT INTO `t_vehicle` VALUES (‘粤B11‘, ‘A‘); INSERT INTO `t_vehicle` VALUES (‘粤B11‘, ‘B‘); INSERT INTO `t_vehicle` VALUES (‘粤B11‘, ‘B‘); INSERT INTO `t_vehicle` VALUES (‘粤B22‘, ‘C‘);
现在要实现一个查询,返回结果如下所示:
这里就涉及到分组查询 ,以及把查询结果的行转换成列的操作,写出来的sql如下:
select t.Vehicle_no, max(CASE t.Type WHEN ‘A‘ THEN t.ct ELSE 0 END ) A_count, max(CASE t.Type WHEN ‘B‘ THEN t.ct ELSE 0 END ) B_count, max(CASE t.Type WHEN ‘C‘ THEN t.ct ELSE 0 END ) C_count from (select Vehicle_no, Type, count(1) ct from t_vehicle group by Vehicle_no, Type)t group by t.Vehicle_no
注意,这里只考虑到了实现功能,而没有考虑sql的查询性能。
标签:分组 sdn ODB splay null rds style end opened
原文地址:https://www.cnblogs.com/zhangxuezhi/p/12013407.html