實現前後行相減的SQL該如何寫？有兩種方法！

針對這類場景，sql語句改如何寫呢？

以統計前後行的訂單號是否連續為例，

表結構：

create table `t_test3` (

`id` int(11) not null auto_increment comment '自增id',
`order_id` int(11) default '0' comment '訂單號',
primary key (`id`),
key (`order_id`)
) engine=innodb  default charset=utf8mb4 comment='';

insert into t_test3(order_id) values(1),(2),(3),(5),(6),(4),(2);

mysql>select *, (select t1.order_id-order_id from t_test3 where order_id=t1.order_id-1 order by order_id desc limit 1) diff from t_test3 t1;

+----+----------+------+
| id | order_id | diff |
+----+----------+------+
|  1 |        1 | null |
|  2 |        2 |    1 |
|  7 |        2 |    1 |
|  3 |        3 |    1 |
|  4 |        5 | null |
|  6 |        5 | null |
|  5 |        6 |    1 |
+----+----------+------+
7 rows in set (0.00 sec)

mysql> select *, (select order_id-t1.order_id from t_test3 where order_id=t1.order_id-1 order by order_id desc limit 1) diff from t_test3 t1 where diff is null;

error 1054 (42s22): unknown column 'diff' in 'where clause'

mysql> select * from t_test3 t1 left join (select * from t_test3  ) t2  on t1.order_id = t2.order_id-1 ;

+----+----------+------+----------+
| id | order_id | id   | order_id |
+----+----------+------+----------+
|  1 |        1 |    2 |        2 |
|  1 |        1 |    7 |        2 |
|  2 |        2 |    3 |        3 |
|  7 |        2 |    3 |        3 |
|  4 |        5 |    5 |        6 |
|  6 |        5 |    5 |        6 |
|  3 |        3 | null |     null |
|  5 |        6 | null |     null |
+----+----------+------+----------+
8 rows in set (0.00 sec)

mysql> select * from t_test3 t1 left join (select * from t_test3  ) t2  on t1.order_id = t2.order_id-1 where t2.order_id is null;

+----+----------+------+----------+
| id | order_id | id   | order_id |
+----+----------+------+----------+
|  3 |        3 | null |     null |
|  5 |        6 | null |     null |
+----+----------+------+----------+
2 rows in set (0.00 sec)

一定要注意欄位的型別，如果是字串型別，又涉及到運算的則可能不會使用到索引。需要強轉回char比較

select u1.id,u1.detail_id,(select detail_id from t_order_detail where status=1 and create_time>='2019-01-09 16:00:00' 

and create_time<='2019-01-09 16:01:00' 
-- 型別轉換
and convert((cast(detail_id as signed)-1),char(100))=u1.detail_id
) as diff
from t_order_detail u1 where status=1  
and create_time>='2019-01-09 16:00:00' 
and create_time<='2019-01-09 16:10:00';

select u1.id,u2.id,u1.detail_id,u2.detail_id  from t_order_detail u1 right join   

(select id,convert((cast(detail_id as signed)-1),char(100)) detail_id from t_order_detail where status=1  
and create_time>='2019-01-09 16:00:00' 
and create_time<='2019-01-09 16:01:00')  u2 
on u1.detail_id=u2.detail_id where u1.detail_id is null  limit 100;

我的訂單前後端實現

功能描述 獲取當前使用者訂單列表 author cakin date 2021 1 3 param request http請求 return r 返回給前端的資料 apioperation value 獲取當前使用者訂單列表 介面 功能描述 獲取當前使用者訂單列表 author cakin dat...

用nginx實現前後端分離的專案的前後端訪問

現在幾乎都是前後端分析的專案，在開發和線上一般都會使用nginx做 來實現跨域和負債均衡。nginx安裝前面已經講過，現在寫寫如何配置，前端技術為vue。server location web server location web 前端 在路徑 var www html yanwei privat...

WebSocket 實現前後端通訊的筆記

引入依賴 在 spring 中要使用 websocket 功能，需要在pom中引入依賴 org.springframework.bootgroupid spring boot starter websocketartifactid dependency 配置類 增加乙個配置類，用於定義 websoc...