创建表
import MySQLdb def connect_mysql(): db_config = { 'host': '192.168.1.5', 'port': 3306, 'user': 'wxp', 'passwd': '1qazXSW@', 'db': 'python', 'charset': 'utf8' } cnx = MySQLdb.connect(**db_config) return cnx if __name__ == '__main__': cnx = connect_mysql() cus = cnx.cursor() # sql = '''insert into student(id, name, age, gender, score) values ('1001', 'ling', 29, 'M', 88), ('1002', 'ajing', 29, 'M', 90), ('1003', 'xiang', 33, 'M', 87);''' #创建表 student = '''create table Student( StdID int not null, StdName varchar(100) not null, Gender enum('M', 'F'), Age tinyint )''' course = '''create table Course( CouID int not null, CName varchar(50) not null, TID int not null )''' score = '''create table Score( SID int not null, StdID int not null, CID int not null, Grade int not null )''' thearch = '''create table Teacher( TID int not null, TName varchar(100) not null )''' #set @i := 0; create table tmp as select (@i := @i + 1) as id from information_schema.tables limit 10; mysql中变量不用事前申明,在用的时候直接用“@变量名”使用就可以了。set这个是mysql中设置变量的特殊用法,当@i需要在select中使用的时候,必须加:,这样就创建好了一个表tmp,查看tmp的数据: tmp = '''set @i := 0; create table tmp as select (@i := @i + 1) as id from information_schema.tables limit 10; ''' try: #cus.execute(student) #cus.execute(course) #cus.execute(score) cus.execute(thearch) cus.execute(tmp) cus.close() cnx.commit() except Exception as e: cnx.rollback() print('error') raise e finally: cnx.close() 输出结果: #查看表 mysql> show tables; +------------------+ | Tables_in_python | +------------------+ | Course | | Score | | Student | | Teacher | | employees | | test | | tmp | +------------------+ 7 rows in set (0.00 sec) #查看表数据 mysql> select * from tmp; +------+ | id | +------+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 10 | +------+ 10 rows in set (0.00 sec)
增加数据 import MySQLdb def connect_mysql(): db_config = { 'host': '192.168.1.5', 'port': 3306, 'user': 'wxp', 'passwd': '1qazXSW@', 'db': 'python', 'charset': 'utf8' } cnx = MySQLdb.connect(**db_config) return cnx if __name__ == '__main__': cnx = connect_mysql() students = '''set @i := 10000; insert into Student select @i:=@i+1, substr(concat(sha1(rand()), sha1(rand())), 1, 3 + floor(rand() * 75)), case floor(rand()*10) mod 2 when 1 then 'M' else 'F' end, 25-floor(rand() * 5) from tmp a, tmp b, tmp c, tmp d; ''' course = '''set @i := 10; insert into Course select @i:=@i+1, substr(concat(sha1(rand()), sha1(rand())), 1, 5 + floor(rand() * 40)), 1 + floor(rand() * 100) from tmp a; ''' score = '''set @i := 10000; insert into Score select @i := @i +1, floor(10001 + rand()*10000), floor(11 + rand()*10), floor(1+rand()*100) from tmp a, tmp b, tmp c, tmp d; ''' theacher = '''set @i := 100; insert into Teacher select @i:=@i+1, substr(concat(sha1(rand()), sha1(rand())), 1, 5 + floor(rand() * 80)) from tmp a, tmp b; ''' try: cus_students = cnx.cursor() cus_students.execute(students) cus_students.close() cus_course = cnx.cursor() cus_course.execute(course) cus_course.close() 输出结果: mysql> select count(*) from Student; +----------+ | count(*) | +----------+ | 10000 | +----------+ 1 row in set (0.00 sec) mysql> select count(*) from Course; +----------+ | count(*) | +----------+ | 10 | +----------+ 1 row in set (0.00 sec) mysql> select count(*) from Score; +----------+ | count(*) | +----------+ | 10000 | +----------+ 1 row in set (0.01 sec) mysql> select count(*) from Teacher; +----------+ | count(*) | +----------+ | 100 | +----------+ 1 row in set (0.00 sec) 如图所示,在Student的表中增加了10000条数据,id是从10000开始的。count函数时用来统计个数的。
解释;
我们知道Student有四个字段,StdID,StdName,Gender,Age;我们先来看这个select语句:select @i:=@i+1, substr(concat(sha1(rand()), sha1(rand())), 1, 3+floor(rand() * 75)), case floor(rand()*10) mod 2 when 1 then 'M' else 'F' end, 25-floor(rand() * 5) from tmp a, tmp b, tmp c, tmp d;
StdID字段:@i就代表的就是,从10000开始,在上一句sql中设置的;
StdName字段:substr(concat(sha1(rand()), sha1(rand())), 1, floor(rand() * 80))就代表的是,
substr是一个字符串函数,从第二个参数1,开始取字符,取到3+ floor(rand() * 75)结束
floor函数代表的是去尾法取整数。
rand()函数代表的是从0到1取一个随机的小数。
rand() * 75就代表的是:0到75任何一个小数,
3+floor(rand() * 75)就代表的是:3到77的任意一个数字
concat()函数是一个对多个字符串拼接函数。
sha1是一个加密函数,sha1(rand())对生成的0到1的一个随机小数进行加密,转换成字符串的形式。
concat(sha1(rand()), sha1(rand()))就代表的是:两个0-1生成的小数加密然后进行拼接。
substr(concat(sha1(rand()), sha1(rand())), 1, floor(rand() * 80))就代表的是:从一个随机生成的一个字符串的第一位开始取,取到(随机3-77)位结束。
Gender字段:case floor(rand()*10) mod 2 when 1 then 'M' else 'F' end,就代表的是,
floor(rand()*10)代表0-9随机取一个数
floor(rand()*10) mod 2 就是对0-9取得的随机数除以2的余数,
case floor(rand()*10) mod 2 when 1 then 'M' else 'F' end,代表:当余数为1是,就取M,其他的为F
Age字段:25-floor(rand() * 5)代表的就是,25减去一个0-4的一个整数
现在有一个问题,为什么会出现10000条数据呢,这10000条数据时怎么生成的呢,虽然字段一一对应上了,但是怎么出来这么多数据呢?
先来看个例子:
select * from tmp a, tmp b, tmp c;
最终是1000条数据,试试有一些感觉了呢,a, b, c都是tmp表的别名,相当于每个表都循环了一遍。所以最终的数据是有多少个表,就是10的多少次幂。
查询数据 import codecs import MySQLdb def connect_mysql(): db_config = { 'host': '192.168.1.5', 'port': 3306, 'user': 'wxp', 'passwd': '1qazXSW@', 'db': 'python', 'charset': 'utf8' } cnx = MySQLdb.connect(**db_config) return cnx if __name__ == '__main__': cnx = connect_mysql() sql = '''select * from Student where StdName in (select StdName from Student group by StdName having count(1)>1 ) order by StdName;''' try: cus = cnx.cursor() cus.execute(sql) result = cus.fetchall() with codecs.open('select.txt', 'w+') as f: for line in result: f.write(str(line)) f.write(' ') cus.close() cnx.commit() except Exception as e: cnx.rollback() print('error') raise e finally: cnx.close() 输出结果 select.txt 文件中 (13565L, u'1d5', u'M', 21) (18739L, u'1d5', u'F', 25) (11564L, u'2d4', u'F', 25) (16082L, u'2d4', u'M', 21) (14565L, u'631', u'M', 21) (17506L, u'631', u'M', 21)
解释:
- 我们先来分析一下select查询这个语句:
select * from Student where StdName in (select StdName from Student group by StdName having count(1)>1 ) order by StdName;'
- 我们先来看括号里面的语句:select StdName from Student group by StdName having count(1)>1;这个是把所有学生名字重复的学生都列出来,
- 最外面select是套了一个子查询,学生名字是在我们()里面的查出来的学生名字,把这些学生的所有信息都列出来。
- result = cus.fetchall()列出结果以后,我们通过fetchall()函数把所有的内容都取出来,这个result是一个tuple
- 通过文件写入的方式,我们把取出来的result写入到select.txt文件中。得到最终的结果。