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)