Python3 notes

where 条件语句

如果我们要读取指定条件的数据，可以使用 where 语句：

demo_mysql_test.py

读取 name 字段为 RUNOOB 的记录：

importmysql.connectormydb = mysql.connector.connect(  host="localhost",   user="root",   passwd="123456",   database="runoob_db")mycursor = mydb.cursor()sql = "SELECT * FROM sites WHERE name ='RUNOOB'"mycursor.execute(sql)myresult = mycursor.fetchall()forxinmyresult:   print(x)

执行代码，输出结果为：

(1,'RUNOOB','https://www.runoob.com')

也可以使用通配符 %：

demo_mysql_test.py

importmysql.connectormydb = mysql.connector.connect(  host="localhost",   user="root",   passwd="123456",   database="runoob_db")mycursor = mydb.cursor()sql = "SELECT * FROM sites WHERE url LIKE '%oo%'"mycursor.execute(sql)myresult = mycursor.fetchall()forxinmyresult:   print(x)

执行代码，输出结果为：

(1,'RUNOOB','https://www.runoob.com')

(2,'Google','https://www.google.com')

为了防止数据库查询发生 SQL 注入的攻击，我们可以使用 %s 占位符来转义查询的条件：

demo_mysql_test.py

importmysql.connectormydb = mysql.connector.connect(  host="localhost",   user="root",   passwd="123456",   database="runoob_db")mycursor = mydb.cursor()sql = "SELECT * FROM sites WHERE name = %s"na = ("RUNOOB", )mycursor.execute(sql, na)myresult = mycursor.fetchall()forxinmyresult:   print(x)