工作遇到问题,需要从大量的数据中筛选出最新的一条数据,但是数据属于不同的对象。也就是获取不同对象的最新一条数据。
上例子:
create table `test` (
`id` int (11),
`company_name` varchar (2295),
`type` varchar (2295),
`create_date` datetime
);
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('1','腾讯','3','2019-10-06 14:06:48');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('2','阿里巴巴','1','2019-10-18 14:35:11');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('3','百度','4','2019-10-06 14:35:16');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('4','小米','7','2019-10-26 14:35:20');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('5','华为','8','2019-10-06 14:35:25');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('6','农业银行','9','2019-10-06 14:35:28');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('7','工商银行','6','2019-10-10 14:35:32');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('8','兴业银行','10','2019-10-23 14:35:36');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('9','浦发银行','5','2019-10-06 14:35:40');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('10','贵州茅台','2','2019-10-06 14:35:44');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('11','腾讯','3','2021-10-06 14:06:48');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('12','阿里巴巴','1','2020-10-18 14:35:11');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('13','百度','4','2021-10-06 14:35:16');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('14','小米','7','2021-10-26 14:35:20');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('15','华为','8','2021-10-06 14:35:25');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('16','农业银行','9','2021-09-06 14:35:28');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('17','工商银行','6','2018-10-10 14:35:32');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('18','兴业银行','10','2020-10-23 14:35:36');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('19','浦发银行','5','2021-10-06 14:35:40');
insert into `test` (`id`, `company_name`, `type`, `create_date`) values('20','贵州茅台','2','2021-10-06 14:35:44');
SELECT * FROM test t RIGHT JOIN (SELECT TYPE, MAX(create_date) AS sj FROM test GROUP BY TYPE) tmp ON (t.create_date = tmp.sj AND t.type=tmp.type)
查询之后的结果:
缺点:使用max效率差很多