MYSQL insert data primary key id is not continuous

Prerequisites

structure

mysql> desc tt1;
+-------+-------------+------+-----+---------+----------------+
| Field | Type        | Null | Key | Default | Extra          |
+-------+-------------+------+-----+---------+----------------+
| id    | int(11)     | NO   | PRI | NULL    | auto_increment |
| name  | varchar(20) | NO   | UNI | NULL    |                |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

content

mysql> select * from tt1;
+----+------+
| id | name |
+----+------+
|  1 | aaa  |
+----+------+
1 row in set (0.00 sec)

Error inserting duplicate records
mysql> insert into tt1 (name)values('aaa');
ERROR 1062 (23000): Duplicate entry 'aaa' for key 'name'


re-operate after modification


mysql> insert into tt1 (name)values( 'bbb');
Query OK, 1 row affected (0.00 sec)

see the content again

mysql> select * from tt1;
+----+------+
| id | name |
+----+------+
|  1 | aaa  |
| 3 | bbb |
+----+------+
2 rows in set (0.00 sec)

Problem: id is not the 2 we need, but 3


reasons: wrong insert operation, which has affected the operation of auto-increment + 1, the
     command is correct, but the data does not meet the table requirements.
     As long as the command is good, auto-increment + 1 Running, no problem.


Solution Before
each insert, set auto_increment=1
, that is, run two commands to complete the correct operation


alter table tt1 auto_increment=1;
        insert into tt1 (name)values('ccc'); The


execution is as follows:

mysql> alter table tt1 auto_increment=1;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0


mysql> insert into tt1 (name)values('ccc');
Query OK, 1 row affected (0.00 sec)

mysql> select * from tt1;
+----+------+
| id | name |
+----+------+
|  1 | aaa  |
| 3 | bbb |
| 4 | ccc |
+----+------+
3 rows in set (0.00 sec)t