爬虫文件存储-1：mysql

1.连接并创建数据库

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306)
cursor = db.cursor()
cursor.execute('SELECT VERSION()')
data = cursor.fetchone()
print('Database version:', data)
cursor.execute("CREATE DATABASE spiders DEFAULT CHARACTER SET utf8")
db.close()

执行结果：

Database version: ('5.7.23',)

结果是创建一个名为spiders的数据库

2.创建数据表

注意：这次连接数据库时需要指定创建数据表所在的数据库，也就是db参数的值

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

sql = 'CREATE TABLE IF NOT EXISTS students (id VARCHAR(255) NOT NULL, name VARCHAR(255) NOT NULL, age INT NOT NULL, PRIMARY KEY (id))'
cursor.execute(sql)
db.close()

3.插入一条数据

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

id = ''
user = 'Bob'
age = 20

sql = 'INSERT INTO students(id, name, age) values(%s, %s, %s)'
try:
    cursor.execute(sql, (id, user, age))
    db.commit()
except:
    db.rollback()
db.close()

通用写法：

这样一来，若是写入更多值的话直接给data字典增加数据就行了，就不用其他sql语句了，推荐使用

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

table = 'students'

data = {
    'id': '',
    'name': 'Bob11',
    'age': 200
}

keys = ', '.join(data.keys())
values = ', '.join(['%s'] * len(data))

sql = 'INSERT INTO {table} ({keys}) VALUES ({values})'.format(table=table, keys=keys, values=values)
try:
    if cursor.execute(sql, tuple(data.values())):
        print('Successful')
        db.commit()
except:
    print('Failed')
    db.rollback()
db.close()

4.更新数据

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

sql = 'UPDATE students SET age = %s WHERE name = %s'
try:
   cursor.execute(sql, (25, 'Bob'))
   db.commit()
except:
   db.rollback()
db.close()

通用写法：

根据主键进行判断，若主键存在则更新，若不存在则插入，推荐使用

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

table = 'students'

data = {
    'id': '',
    'name': 'Bob',
    'age': 21
}

keys = ', '.join(data.keys())
values = ', '.join(['%s'] * len(data))

sql = 'INSERT INTO {table}({keys}) VALUES ({values}) ON DUPLICATE KEY UPDATE'.format(table=table, keys=keys,
                                                                                     values=values)
update = ','.join([" {key} = %s".format(key=key) for key in data])
sql += update
try:
    if cursor.execute(sql, tuple(data.values()) * 2):
        print('Successful')
        db.commit()
except:
    print('Failed')
    db.rollback()
db.close()

5.删除数据

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

table = 'students'
condition = 'age > 20'

sql = 'DELETE FROM  {table} WHERE {condition}'.format(table=table, condition=condition)
try:
    cursor.execute(sql)
    db.commit()
except:
    db.rollback()

db.close()

6.查询数据

import pymysql

db = pymysql.connect(host='localhost', user='root', password='root', port=3306, db='spiders')
cursor = db.cursor()

sql = 'SELECT * FROM students WHERE age >= 20'
try:
    cursor.execute(sql)
    print('Count:', cursor.rowcount)
    row = cursor.fetchone()
    while row:
        print('Row:', row)
        row = cursor.fetchone()
except:
    print('Error')