MySQL及MyBatis问题汇总

1 外键

1.0 外键必须是另一个表的主键或唯一键.

int goods_id unique,
int goods_infos auto_increment

1.2 同一个数据库外键命名唯一

Cannot add or update a child row: a foreign key constraint fails (peopleinfosforsb.vacancy_timers, CONSTRAINT vacancy_timers_ibfk_1 FOREIGN KEY (task_name) REFERENCES vacancy_tasks (task_name) ON DELETE CASCADE ON UPDATE CASCADE

• 原因
  外键重名,添加或更新外键表数据时,主表中不含该外键数据.
• 解决
  修改外键名,使同一个数据库中的表中外键名唯一.先添加主表数据,再添加子表数据.

1.3 主表先添加数据再更新子表数据

Cannot add or update a child row: a foreign key constraint fails (peopleinfosforsb.vacancy_timers, CONSTRAINT vacancy_timers_ibfk_1 FOREIGN KEY (task_name) REFERENCES vacancy_tasks (task_name) ON DELETE CASCADE ON UPDATE CASCADE

• 原因
  添加或更新外键表数据时,主表中不含该外键数据.
• 解决
  先添加主表数据,再添加子表数据.

2 mysql使用关键字报错

Error updating database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'group, name)

• 原因
  使用了关键字group.
• 解决
  遇到关键字,修改.

3 mybatis找不到string

nested exception is org.apache.ibatis.reflection.ReflectionException: There is no getter for property named ‘task_name’ in ‘class java.lang.String’
-原因
未设置字符键值对.

• 解决
  设置字符键值对.

4 mysql数据库连接失败

ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (2)

5 pymysql连接失败

sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (1045, “Access denied for user ‘root’@‘localhost’ (using password: YES)”)

6 MySQL语句执行时，Mybatis数据类型不兼容

invalid comparison: java.util.ArrayList and java.lang.String
场景：传入数据为list（Array），参数比较时，使用了字符比较
参数：List nameLis=Array.asList(“xiaoxiao”,“xiaohua”);
Mybatis比较形式：

<if test="nameLis != null and nameLis !=''">
  and name in 
  <foreach collection="nameLis" index="index" item="item" open="(" separator="," close=")">
    #{item}
  </foreach>
</if>

nameLis为List类型，而nameLis != ''是字符串比较，因此报错，
正确形式为：

<if test="nameLis != null and nameLis.size()>0">
  and name in 
  <foreach collection="nameLis" index="index" item="item" open="(" separator="," close=")">
    #{item}
  </foreach>
</if>

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【参考文献】
[1]https://www.cnblogs.com/liushui-sky/p/8830936.html
[2]https://blog.csdn.net/qq_41042595/article/details/88591028
[3]https://blog.csdn.net/hmmmmm2929/article/details/93193394
[4]https://www.jianshu.com/p/9152bcbd0e91
[5]https://www.cnblogs.com/orac/p/6726323.html
[6]http://www.cnntt.com/archives/2505
[7]https://blog.csdn.net/qq_43642812/article/details/89578126
[8]https://www.cnblogs.com/zyulike/p/10542341.html

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