mysql踩过的坑

1. ERROR 1146 (42S02): Table 'test.user' doesn't exist
   • 删除用户不存在
2. ERROR 1215 (HY000): Cannot add foreign key constraint
   • 被关联字段必须是至少是有unique约束的，没有则报错
3. ERROR 1062 (23000): Duplicate entry '1' for key 'id'
   • 有unique约束，插入数据重复
4. ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
   • auto_increment字段必须定义一个键(key)，primary或unique
5. ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (test.test_1_1, CONSTRAINT fk_test_1 FOREIGN KEY (id) REFERENCES test_1 (id) ON DELETE SET NULL ON UPDATE CASCADE)
   • 被关联的表中没有数据
6. ERROR 1064 (42000): 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 'foreign key(teacher_id) references teacher(tid) on delete cascade on update cascade' at line 1
   • 别关联的表中必须有数据才能够关联，不然会报错
7. ERROR 1022 (23000): Can't write; duplicate key in table '#sql-13ce_5'
   • 使用alter添加约束的名称和已经存在的约束名称相同
8. ERROR 1364 (HY000): Field 'age' doesn't have a default value
   • age字段没有默认值
9. ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'day40.employee.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
   • 必须有group的字段
10. ERROR 1093 (HY000): You can't specify target table 'book' for update in FROM clause
11. ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'day40.staff.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
12. ERROR 1242 (21000): Subquery returns more than 1 row
    • 子查询返回值为多个
13. ERROR 1052 (23000): Column 'sid' in field list is ambiguous
    • sid字段位置模糊，通常须要给table命别名，或者使用具题table’s name指定便可
14. ERROR 1248 (42000): Every derived table must have its own alias
    • 每一个初始表必须有一个别名
15. ERROR 1630 (42000): FUNCTION t2.max does not exist. Check the 'Function Name Parsing and Resolution' section in the Reference Manual
    • 若是使用聚合函数获得的值，须要手动指定名称
16. pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1' ([Errno 61] Connection refused)")
    • 经过socket链接mysql出错，一般是默认参数和传参出现问题
    • 默认端口号3306，能够经过sudo lsof -i:3306查看
    • host中能够使用localhost或127.0.0.1测试
17. AttributeError: 'module' object has no attribute 'connect'
    • 模块是否正确安装，若是已经安装
    • 检查py文件名和模块名重复
18. pymysql.err.OperationalError: (1044, "Access denied for user 'guest'@'%' to database 'test'")
    • 一般是connect中的参数有误
19. pymysql.err.OperationalError: (1045, "Access denied for user 'guest'@'192.168.0.103' (using password: YES)")
    • 一般是链接参数有误