mysql中数据类型不一样用IF查会出错

最新推荐文章于 2024-06-29 16:15:57 发布

HackProgramer

最新推荐文章于 2024-06-29 16:15:57 发布

阅读量429

点赞数

分类专栏： Mysql

Mysql 专栏收录该内容

53 篇文章

订阅专栏

本文展示了在Windows XP环境下使用MySQL命令行工具进行的一系列操作，包括登录数据库、选择数据库、查看表结构、修改表结构及查询数据等过程。通过本文可以了解基本的MySQL命令语法。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Microsoft Windows XP [版本 5.1.2600]
(C) 版权所有 1985-2001 Microsoft Corp.

C:\Documents and Settings\Administrator>mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.5.36 MySQL Community Server (GPL)

Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use sondome;
ERROR 1049 (42000): Unknown database 'sondome'
mysql> use sondemo;
Database changed
mysql> show tables;
+--------------------+
| Tables_in_sondemo |
+--------------------+
| info_user          |
| info_user_consumer |
+--------------------+
2 rows in set (0.00 sec)

mysql> alter info_user add C_id int;
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 'info_user add C_id int' at line 1
mysql> alter table info_user add column C_id int not null;
Query OK, 3 rows affected (0.08 sec)
Records: 3 Duplicates: 0 Warnings: 0

mysql> desc info_user;
+--------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+--------+--------------+------+-----+---------+----------------+
| U_id   | int(11)      | NO   | PRI | NULL    | auto_increment |
| U_name | varchar(100) | NO   |     | NULL    |                |
| C_id   | int(11)      | NO   |     | NULL    |                |
+--------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

mysql> select if(C_id,C_id,U_id) as chuan,C_id from info_user;
+-------+------+
| chuan | C_id |
+-------+------+
|     1 |    0 |
|     2 |    0 |
|     3 |    0 |
+-------+------+
3 rows in set (0.00 sec)

mysql>