自关联与not exists，查询出最大年段的客户信息

所用数据库mysql5.7

1、创建表：create table query1(id int not null auto_increment,custId varchar(6),startYear varchar(6),primary key(id))

 2、插入数据：

INSERT into query1 (custId,startYear) VALUES 
('1','1990'),
('1','1991'),
('1','1992'),
('1','2000'),
('1','2002'),
('1','2002'),
('2','1990'),
('3','1990'),
('3','1990'),
('4','1990'),
('4','1991'),
('4','1992'),
('4','2000'),
('4','2008'),
('4','2008'),
('5','1990'),
('5','1991'),
('5','2000'),
('5','2000'),
('5','2008'),
('5','2008')

3、sql：

select distinct q1.custId,q1.startYear from query1 q1 WHERE
not exists (select '1' from query1 q2 WHERE q1.custId=q2.custId and q1.startYear<q2.startYear)

查看结果：

 由于同一个custId可以存着重复的年段，所以用distinct去重