-- 1、得到每个分组中id最小的那条记录

 select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03'

 group by point_code

 -- 37033746    XX00016    长江大桥路口    http://xxx/10.58.237.73_01_20180903001241103.jpg    2018-09-03 00:12:41

 -- 37033631    XX00024    沱六桥路口    http://xxx/10.25.77.3_01_20180903000355528.jpg    2018-09-03 00:03:55

 -- 37033485    XX00025    高新区立交桥    http://xxx/10.210.98.143_01_20180903000211230.jpg    2018-09-03 00:02:11

 -- 2、意图，先通过子查询，按照ID降序，得到每个分组中最新的一条记录

 select * from

 (

     select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03' order by id desc -- limit 1000

 ) tt

 group by point_code;

 -- 结果还是每个分组最小的记录，与第一种写法结果相同

 -- 3、在第二种写法的子查询周添加了一个limit，limit后面的数字大于你查询的总条数即可

 select * from

 (

     select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03' order by id desc limit 10000000000

 ) tt

 group by point_code;

 -- 结果返回每个分组中最新的那条记录

 -- 37064239    XX00016    长江大桥路口    http://xxx/10.58.237.73_01_20180903144242037.jpg    2018-09-03 14:42:42

 -- 37064240    XX00024    沱六桥路口    http://xxx/10.25.77.3_01_20180903143857383.jpg    2018-09-03 14:38:57

 -- 37064139    XX00025    高新区立交桥    http://xxx/10.210.98.143_01_20180903143713651.jpg    2018-09-03 14:37:13

 -- 4、在第一中写法的group by后面添加一个desc

 select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03'

 group by point_code desc

 -- 返回结果是每个分组的最新记录

 -- 37064139    XX00025    高新区立交桥    http://xxx/10.210.98.143_01_20180903143713651.jpg    2018-09-03 14:37:13

 -- 37064240    XX00024    沱六桥路口    http://xxx/10.25.77.3_01_20180903143857383.jpg    2018-09-03 14:38:57

 -- 37064239    XX00016    长江大桥路口    http://xxx/10.58.237.73_01_20180903144242037.jpg    2018-09-03 14:42:42

 -- 5、一般我们在查询结果都会按照一定规则进行排序，对第四种写法进行排序

 select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03'

 group by point_code desc order by point_code

 -- 返回结果又变成了每个分组的最小记录了

 -- 37033746    XX00016    长江大桥路口    http://xxx/10.58.237.73_01_20180903001241103.jpg    2018-09-03 00:12:41

 -- 37033631    XX00024    沱六桥路口    http://xxx/10.25.77.3_01_20180903000355528.jpg    2018-09-03 00:03:55

 -- 37033485    XX00025    高新区立交桥    http://xxx/10.210.98.143_01_20180903000211230.jpg    2018-09-03 00:02:11

 -- 6、将第五种写法的排序，放到分组外边

 select * from

 (

     select * from pic where point_code in('XX00024', 'XX00016', 'XX00025') and addtime > '2018-09-03'

     group by point_code desc

 ) t order by point_code

 -- 返回的结果又是每个分组的最新值

 -- 37064239    XX00016    长江大桥路口    http://xxx/10.58.237.73_01_20180903144242037.jpg    2018-09-03 14:42:42

 -- 37064240    XX00024    沱六桥路口    http://xxx/10.25.77.3_01_20180903143857383.jpg    2018-09-03 14:38:57

 -- 37064139    XX00025    高新区立交桥    http://xxx/10.210.98.143_01_20180903143713651.jpg    2018-09-03 14:37:13