mysql的小常识

为了爬虫的需要，稍微预习一下mysql；

选择当前的数据库后，查看数据库信息用：

USE;

删除：DROP DATABASE spiders

#删除name为spiders的的数据库

选择：SELECT *FROM users

 mysql> USE spiders;
 Database changed
 mysql> DESC users;
 +----------+--------------+------+-----+---------+----------------+
 | Field    | Type         | Null | Key | Default | Extra          |
 +----------+--------------+------+-----+---------+----------------+
 | Id       | int(11)      | NO   | PRI | NULL    | auto_increment |
 | email    | varchar(255) | YES  |     |         |                |
 | password | varchar(255) | YES  |     | NULL    |                |
 +----------+--------------+------+-----+---------+----------------+
 3 rows in set (0.04 sec)

 mysql> SELECT * FROM users
     -> ;
 +----+----------------------+-------------+
 | Id | email                | password    |
 +----+----------------------+-------------+
 |  1 | webmaster@python.org | very-secret |
 |  2 | webmaster@python.org | very-secret |
 |  3 | webmaster@python.org | very-secret |
 |  4 | webmaster@python.org | very-secret |
 |  5 | webmaster@python.org | very-secret |
 |  6 | webmaster@python.org | very-secret |
 |  7 | webmaster@python.org | very-secret |
 +----+----------------------+-------------+
 7 rows in set (0.00 sec)

cha查看数据库中的表：SHOW TABLES

 mysql> SHOW TABLES;
 +-------------------+
 | Tables_in_spiders |
 +-------------------+
 | kandong           |
 | stu               |
 | users             |
 +-------------------+
 3 rows in set (0.00 sec)

 mysql> ALTER TABLE kandong ADD sha INT(10);
 Query OK, 0 rows affected (0.27 sec)
 Records: 0  Duplicates: 0  Warnings: 0
 mysql> DESC  kandong;
 +-------+--------------+------+-----+---------+-------+
 | Field | Type         | Null | Key | Default | Extra |
 +-------+--------------+------+-----+---------+-------+
 | id    | varchar(255) | NO   | PRI | NULL    |       |
 | name  | varchar(255) | NO   |     | NULL    |       |
 | age   | int(11)      | NO   |     | NULL    |       |
 | sha   | int(10)      | YES  |     | NULL    |       |
 +-------+--------------+------+-----+---------+-------+
 4 rows in set (0.03 sec)