MySQL数据库删除数据后自增ID不连续的问题及解决

SET @auto_id = 0;
UPDATE 表名 SET 自增字段名 = (@auto_id := @auto_id + 1);
ALTER TABLE 表名 AUTO_INCREMENT = 1;

//删除信息
    public void delete(int id) {
        try {
            PreparedStatement ps = con.prepareStatement("delete from books where id = ?");
            ps.setInt(1, id);
            ps.executeUpdate();
            PreparedStatement pr = con.prepareStatement("alter table books auto_increment = ?;");
            pr.setInt(1, id - 1);
            pr.executeUpdate();
 
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

mysql> CREATE TABLE tb_student3(
    -> id INT PRIMARY KEY AUTO_INCREMENT,
    -> name VARCHAR(20) UNIQUE KEY,
    -> age INT DEFAULT NULL);
Query OK, 0 rows affected (0.02 sec)

mysql> INSERT INTO tb_student3 VALUES(1,'1','1');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO tb_student3 VALUES(NULL,'1','1');
ERROR 1062 (23000): Duplicate entry '1' for key 'name'

ERROR 1062 (23000): Duplicate entry '1' for key 'name'
mysql> INSERT INTO tb_student3 VALUES(NULL,'2','1');
Query OK, 1 row affected (0.01 sec)

mysql> SELECT * FROM tb_student3;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | 1    |    1 |
|  3 | 2    |    1 |
+----+------+------+
2 rows in set (0.00 sec)

#创建新表
mysql> CREATE TABLE IF NOT EXISTS tb_student4(
    -> id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    -> name VARCHAR(10) NOT NULL);
Query OK, 0 rows affected (0.02 sec)

#新增字段
mysql> INSERT INTO tb_student4(name) VALUES('JAVA'),('PYTHON');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

#查看表内容
mysql> SELECT * FROM tb_student4;
+----+--------+
| id | name   |
+----+--------+
|  1 | JAVA   |
|  2 | PYTHON |
+----+--------+
2 rows in set (0.00 sec)

#删除字段 name='PYTHON'
mysql> DELETE FROM tb_student4 WHERE name='PYTHON';
Query OK, 1 row affected (0.01 sec)

#查看表内容
mysql> SELECT * FROM tb_student4;
+----+------+
| id | name |
+----+------+
|  1 | JAVA |
+----+------+
1 row in set (0.00 sec)

#插入表数据
mysql> INSERT INTO tb_student4(name) VALUES('MYSQL'),('HTML');
Query OK, 2 rows affected (0.01 sec)
Records: 2  Duplicates: 0  Warnings: 0

#查看表内容
mysql> SELECT * FROM tb_student4;
+----+-------+
| id | name  |
+----+-------+
|  1 | JAVA  |
|  3 | MYSQL |
|  4 | HTML  |
+----+-------+
3 rows in set (0.00 sec)

SET @i=0;

UPDATE `tablename` SET `id`=(@i:=@i+1);

ALTER TABLE `tablename` AUTO_INCREMENT=0

mysql> SET @i=0;
Query OK, 0 rows affected (0.00 sec)
mysql> UPDATE `tb_student3` SET `id`=(@i:=@i+1);
Query OK, 1 row affected (0.02 sec)
Rows matched: 2  Changed: 1  Warnings: 0
mysql> ALTER TABLE `tb_student3` AUTO_INCREMENT=0
    -> ;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0mysql> select * from tb_student3;
+----+------+------+
| id | name | age  |
+----+------+------+
|  1 | 1    |    1 |
|  2 | 2    |    1 |
+----+------+------+
2 rows in set (0.00 sec)