通过pymysql操作数据库

 1 import pymysql
 2 user=input("username:")
 3 pwd=input("password:")
 4 conn=pymysql.connect(host="localhost",user="%s"%user,password="",database="db1")#连接数据库
 5 cursor=conn.cursor()#通过游标操作，相当于手
 6 sql="select sid,sname from (select A.oid from (select student_id as oid,num as onum from score left join course on score.course_id=course.cid where cname=‘生物‘)as A left join (select student_id as pid,num as pnum from score left join course on score.course_id=course.cid where cname=‘物理‘)as B on A.oid=B.pid where A.onum>B.pnum)as C left join student on C.oid=student.sid"#表示有名字，可以excute(sql,{"u":user,"p":pwd})
 7 cursor.execute(sql)#通过该语句执行,[]里为自动执行占位符
 8 result=cursor.fetchall()#拿第一个
 9 cursor.close()
10 conn.close()
11 if result:
12     print(result)
13 else:
14     print("用户名或密码错误")