前言: 最近开始学django了，学了下web框架，顿时感觉又会了好多知识。happy~~ 这篇博客整理写下数据库基本操作，内容挺少。明天写SQLAlchemy。
一、数据库基本操作
1. 想允许在数据库写中文，可在创建数据库时用下面命令
create database zcl charset utf8;
2. 查看students表结构
desc students;
3. 查看创建students表结构的语句
show create table students;
4. 删除数据库
drop database zcl;
5. 创建一个新的字段
alter table students add column nal char(64);
PS: 本人是很讨厌上面这种“简单解释+代码”的博客。其实我当时在mysql终端写了很多的实例，不过因为当时电脑运行一个看视频的软件，导致我无法Ctrl+C/V。现在懒了哈哈~~
二、python连接数据库
python3不再支持mysqldb。其替代模块是PyMySQL。本文的例子是在python3.4环境。
1. 安装pymysql模块
pip3 install pymysql
2. 连接数据库，插入数据实例
import pymysql
#生成实例，连接数据库zcl
conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')
#生成游标，当前实例所处状态
cur = conn.cursor()
#插入数据
reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Jack','man',25,1351234,"CN"))
reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Mary','female',18,1341234,"USA"))
conn.commit() #实例提交命令
cur.close()
conn.close()
print(reCount)
查看结果:
mysql> select* from students;+----+------+-----+-----+-------------+------+ | id | name | sex | age | tel | nal | +----+------+-----+-----+-------------+------+ | 1 | zcl | man | 22 | 15622341234 | NULL | | 2 | alex | man | 30 | 15622341235 | NULL | +----+------+-----+-----+-------------+------+ 2 rows in set
3. 获取数据
import pymysql
conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')
cur = conn.cursor()
reCount = cur.execute('select* from students')
res = cur.fetchone() #获取一条数据
res2 = cur.fetchmany(3) #获取3条数据
res3 = cur.fetchall() #获取所有(元组格式)
print(res)
print(res2)
print(res3)
conn.commit()
cur.close()
conn.close()
输出:
(1, 'zcl', 'man', 22, '15622341234', None) ((2, 'alex', 'man', 30, '15622341235', None), (5, 'Jack', 'man', 25, '1351234', 'CN'), (6, 'Mary', 'female', 18, '1341234', 'USA')) ()
三、事务回滚
事务回滚是在数据写到数据库前执行的，因此事务回滚conn.rollback()要在实例提交命令conn.commit()之前。只要数据未提交就可以回滚，但回滚后ID却是自增的。请看下面的例子:
插入3条数据(注意事务回滚):
import pymysql
#连接数据库zcl
conn=pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')
#生成游标，当前实例所处状态
cur=conn.cursor()
#插入数据
reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Jack', 'man', 25, 1351234, "CN"))
reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s,%s,%s,%s,%s)', ('Jack2', 'man', 25, 1351234, "CN"))
reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Mary', 'female', 18, 1341234, "USA"))
conn.rollback() #事务回滚
conn.commit() #实例提交命令
cur.close()
conn.close()
print(reCount)
未执行命令前与执行命令后(包含回滚操作)(注意ID号): 未执行上面代码与执行上面代码的结果是一样的!!因为事务已经回滚，故students表不会增加数据!
mysql> select* from students;+----+------+--------+-----+-------------+------+ | id | name | sex | age | tel | nal | +----+------+--------+-----+-------------+------+ | 1 | zcl | man | 22 | 15622341234 | NULL | | 2 | alex | man | 30 | 15622341235 | NULL | | 5 | Jack | man | 25 | 1351234 | CN | | 6 | Mary | female | 18 | 1341234 | USA | +----+------+--------+-----+-------------+------+ 4 rows in set
执行命令后(不包含回滚操作):只需将上面第11行代码注释。
mysql> select* from students;+----+-------+--------+-----+-------------+------+ | id | name | sex | age | tel | nal | +----+-------+--------+-----+-------------+------+ | 1 | zcl | man | 22 | 15622341234 | NULL | | 2 | alex | man | 30 | 15622341235 | NULL | | 5 | Jack | man | 25 | 1351234 | CN | | 6 | Mary | female | 18 | 1341234 | USA | | 10 | Jack | man | 25 | 1351234 | CN | | 11 | Jack2 | man | 25 | 1351234 | CN | | 12 | Mary | female | 18 | 1341234 | USA | +----+-------+--------+-----+-------------+------+ 7 rows in set
总结：虽然事务回滚了，但ID还是自增了，不会因回滚而取消，但这不影响数据的一致性（底层的原理我不清楚~）
四、批量插入数据
import pymysql
#连接数据库zcl
conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')
#生成游标，当前实例所处状态
cur = conn.cursor()
li = [
("cjy","man",18,1562234,"USA"),
("cjy2","man",18,1562235,"USA"),
("cjy3","man",18,1562235,"USA"),
("cjy4","man",18,1562235,"USA"),
("cjy5","man",18,1562235,"USA"),
]
#插入数据
reCount = cur.executemany('insert into students(name,sex,age,tel,nal) values(%s,%s,%s,%s,%s)', li)
#conn.rollback() #事务回滚
conn.commit() #实例提交命令
cur.close()
conn.close()
print(reCount)
pycharm下输出: 5
mysql终端显示:
mysql> select* from students; #插入数据前+----+-------+--------+-----+-------------+------+ | id | name | sex | age | tel | nal | +----+-------+--------+-----+-------------+------+ | 1 | zcl | man | 22 | 15622341234 | NULL | | 2 | alex | man | 30 | 15622341235 | NULL | | 5 | Jack | man | 25 | 1351234 | CN | | 6 | Mary | female | 18 | 1341234 | USA | | 10 | Jack | man | 25 | 1351234 | CN | | 11 | Jack2 | man | 25 | 1351234 | CN | | 12 | Mary | female | 18 | 1341234 | USA | +----+-------+--------+-----+-------------+------+ 7 rows in set mysql> mysql> select* from students; #插入数据后+----+-------+--------+-----+-------------+------+ | id | name | sex | age | tel | nal | +----+-------+--------+-----+-------------+------+ | 1 | zcl | man | 22 | 15622341234 | NULL | | 2 | alex | man | 30 | 15622341235 | NULL | | 5 | Jack | man | 25 | 1351234 | CN | | 6 | Mary | female | 18 | 1341234 | USA | | 10 | Jack | man | 25 | 1351234 | CN | | 11 | Jack2 | man | 25 | 1351234 | CN | | 12 | Mary | female | 18 | 1341234 | USA | | 13 | cjy | man | 18 | 1562234 | USA | | 14 | cjy2 | man | 18 | 1562235 | USA | | 15 | cjy3 | man | 18 | 1562235 | USA | | 16 | cjy4 | man | 18 | 1562235 | USA | | 17 | cjy5 | man | 18 | 1562235 | USA | +----+-------+--------+-----+-------------+------+ 12 rows in set
学完的东西要及时总结，有些东西忘记了阿~_~
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