mysql 行转列，列转行
1、先创建基础表，添加数据，
CREATE TABLE `t_user` ( `user_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '用户id', `name` varchar(255) DEFAULT NULL COMMENT '名称', `mobile` varchar(100) DEFAULT NULL COMMENT '电话', PRIMARY KEY (`user_id`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; INSERT INTO `test`.`t_user` (`user_id`, `name`, `mobile`) VALUES ('1', '唐僧', '65651615,6111651,51651651,61565161,6156'); INSERT INTO `test`.`t_user` (`user_id`, `name`, `mobile`) VALUES ('2', '悟空', '452651651,478855,41223'); INSERT INTO `test`.`t_user` (`user_id`, `name`, `mobile`) VALUES ('3', '八戒', '325489,3214778,38955,39999'); INSERT INTO `test`.`t_user` (`user_id`, `name`, `mobile`) VALUES ('4', '沙僧', '25555,23333,21111'); CREATE TABLE `t_kill` ( `kill_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'id主键', `number` int(11) DEFAULT NULL COMMENT '杀敌数', `time` datetime DEFAULT NULL COMMENT '时间', `user_id` int(11) DEFAULT NULL COMMENT '用户id', PRIMARY KEY (`kill_id`) ) ENGINE=InnoDB AUTO_INCREMENT=17 DEFAULT CHARSET=utf8; INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('6', '12', '2020-12-27 15:31:23', '2'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('3', '5', '2020-12-26 15:31:23', '1'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('4', '8', '2020-12-25 15:31:23', '1'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('10', '15', '2020-12-24 15:31:23', '3'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('8', '10', '2020-12-18 15:31:23', '2'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('7', '52', '2020-12-08 15:31:23', '2'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('5', '47', '2020-11-28 15:31:23', '2'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('9', '8', '2020-10-27 15:31:23', '3'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('1', '15', '2020-10-18 15:31:23', '1'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('15', '11', '2020-10-17 15:31:23', '4'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('14', '12', '2020-10-16 15:31:23', '4'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('13', '21', '2020-10-15 15:31:23', '4'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('12', '35', '2020-10-11 15:31:23', '3'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('16', '9', '2020-10-10 15:31:23', '4'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('2', '9', '2020-09-26 15:31:23', '1'); INSERT INTO `test`.`t_kill` (`kill_id`, `number`, `time`, `user_id`) VALUES ('11', '24', '2020-09-25 15:31:23', '3');
2.列转行， 使用 case when
-- 查询用户杀敌数 SELECT tu.user_id, tu.`name`, SUM(tk.number) total FROM t_user tu LEFT JOIN t_kill tk ON tu.user_id = tk.user_id GROUP BY tu.name;
-- 使用 case when SELECT sum(CASE WHEN tu.name = '唐僧' then tk.number end) '唐僧', sum(CASE WHEN tu.name = '悟空' then tk.number end) '悟空', sum(CASE WHEN tu.name = '八戒' then tk.number end) '八戒', sum(CASE WHEN tu.name = '沙僧' then tk.number end) '沙僧' FROM t_user tu LEFT JOIN t_kill tk ON tu.user_id = tk.user_id ;
3、行转列
3.1 单行转列：
-- 生成一张序列表
CREATE TABLE `t_sequence` ( `id` int(11) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; -- 行转列，可替换t_user表名和字段使用 SELECT NAME, REPLACE ( SUBSTRING( SUBSTRING_INDEX(mobile, ',', a.id), CHAR_LENGTH( SUBSTRING_INDEX(mobile, ',', a.id - 1) ) + 1 ), ',', '' ) AS moblie FROM t_sequence a CROSS JOIN ( SELECT NAME, CONCAT(mobile, ',') AS mobile, LENGTH(mobile) - LENGTH(REPLACE(mobile, ',', '')) + 1 size FROM t_user b ) b ON a.id <= b.size;
3.1 多行转列：
-- 基础数据 SELECT name,arms,clothing,shoe from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id
-- 使用union all SELECT name,'arms' equipment,arms from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id union all SELECT name,'clothing' equipment,clothing from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id union all SELECT name,'shoe' equipment,shoe from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id
-- 使用序列表 -- 一行变三行 SELECT name,arms,clothing,shoe from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id CROSS join t_sequence ts where ts.id<4 ORDER BY name
使用 case when
SELECT name,
case when ts.id = 1 then 'arms' end,
case when ts.id = 2 then 'clothing' end,
case when ts.id = 3 then 'shoe' end as equipment,
case when ts.id = 1 then arms end,
case when ts.id = 2 then clothing end,
case when ts.id = 3 then shoe end
from t_user tu
LEFT JOIN t_equipment te on tu.user_id = te.user_id
CROSS join t_sequence ts where ts.id<4
ORDER BY name
-- COALESCE 只取非控值 SELECT name, COALESCE(case when ts.id = 1 then 'arms' end, case when ts.id = 2 then 'clothing' end, case when ts.id = 3 then 'shoe' end) as equipment, COALESCE(case when ts.id = 1 then arms end, case when ts.id = 2 then clothing end, case when ts.id = 3 then shoe end) as eq_name from t_user tu LEFT JOIN t_equipment te on tu.user_id = te.user_id CROSS join t_sequence ts where ts.id<4 ORDER BY name;
cross join 学习可观看：https://www.cnblogs.com/mzq123/p/11783698.html
4、分组查询前几条数据
-- 查询每一条数据，cnt是t_kill表中number比当前数据number大的数据的条数 SELECT tu.user_id, tu.`name`, tk.kill_id, tk.number, tk.time, ( SELECT count(1) from t_kill t where t.number > tk.number and t.user_id = tu.user_id) cnt FROM t_user tu LEFT JOIN t_kill tk ON tu.user_id = tk.user_id;
-- 根据cnt查询数据 SELECT * from (SELECT tu.user_id, tu.`name`, tk.kill_id, tk.number, tk.time, ( SELECT count(1) from t_kill t where t.number > tk.number and t.user_id = tu.user_id) cnt FROM t_user tu LEFT JOIN t_kill tk ON tu.user_id = tk.user_id) c where cnt < 2 ORDER BY name , number desc;
