如果希望在每次插入新記錄時，自動地創建主鍵字段的值。可以在表中創建一個 auto-increment 字段。MySQL 使用 AUTO_INCREMENT 關鍵字來執行 auto-increment 任務。默認地AUTO_INCREMENT 的開始值是 1，每條新記錄遞增 1。
主鍵又稱主關鍵字，主關鍵字(primary key)是表中的一個或多個字段，它的值用於唯一地標識表中的某一條記錄。
測試創建一個test表：
mysql> create table test (
aid int not null auto_increment,
site_id int, cout int, date date,
primary key (aid) );
Query OK, 0 rows affected (0.01 sec)
mysql> desc test;
+---------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+----------------+
| aid | int(11) | NO | PRI | NULL | auto_increment |
| site_id | int(11) | YES | | NULL | |
| cout | int(11) | YES | | NULL | |
| date | date | YES | | NULL | |
+---------+---------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql>
嘗試插入兩條數據
mysql> insert into test9 (site_id , cout, date) value ( 1,45,'2019-10-10' ),( 1,45,'2016-05-10' );
Query OK, 2 row affected (0.00 sec)
mysql> select * from test9;
+-----+---------+------+------------+
| aid | site_id | cout | date |
+-----+---------+------+------------+
| 2 | 1 | 45 | 2019-10-10 |
| 4 | 1 | 45 | 2016-05-10 |
+-----+---------+------+------------+
2 rows in set (0.00 sec)
mysql>
發現aid是有自動添加而且遞增，但遞增都是加2.
應該是mysql環境設置問題，auto_increment的默認值是2，更改為1 就行
mysql> set @@global.auto_increment_increment = 1;
Query OK, 0 rows affected (0.01 sec)
mysql> set @@auto_increment_increment =1;
Query OK, 0 rows affected (0.00 sec)
再嘗試添加數據，就可以了
mysql> insert into test9 (site_id , cout, date) value ( 3,55,'2017-05-20' ),( 4,45,'2017-08-20' );
Query OK, 2 row affected (0.00 sec)
mysql> select * from test9;
+-----+---------+------+------------+
| aid | site_id | cout | date |
+-----+---------+------+------------+
| 2 | 1 | 45 | 2019-10-10 |
| 4 | 1 | 45 | 2016-05-10 |
| 5 | 3 | 55 | 2017-05-20 |
| 6 | 4 | 45 | 2017-08-20 |
+-----+---------+------+------------+
4rows in set (0.00 sec)
mysql>