要求：獲得按table1_id分組，並且age最大的記錄資訊，即2、3、5條方法一：select * from (select * from table2 order by age desc) as a group by a.table1_id方法二：select a.* from table2 as a where age = (select max(age) from table2 where a.table1_id=table1_id)方法三：select a.* from table2 as a where not exists (select * from table2 where table1_id=a.table1_id and age>a.age)方法四：select a.* from table2 as a where exists (select count(*) from table2 where table1_id=a.table1_id and age>a.age having count(*)=0)

最近看了下評論都說第一個是錯的，現在我把表結構和資料都發出來。注意：這裡用的是mysql資料庫

CREATE TABLE `table2` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `table1_id` varchar(255) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `aaa` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;



INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('1', '1', '10', 'a1');
INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('2', '1', '20', 'a2');
INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('3', '2', '33', 'a3');
INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('4', '2', '11', 'a4');
INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('5', '3', '55', 'a5');
INSERT INTO `table2` (`id`, `table1_id`, `age`, `aaa`) VALUES ('6', '3', '44', 'a6');
 

我不保證有啥特殊情況會產生啥其他問題，但就我上面的例子來說沒看出什麼毛病。