Python連接MySQL數據庫

#coding:utf-8
import  mysql.connector
#D:\chrome download\mysql-5.7.29-winx64\mysql-5.7.29-winx64\data
#打開這個data文件夾，找到一個類型爲err的文件，用記事本打開，裏面有句A temporary password is generated for root@localhost:這個後面記錄的就是你的初始密碼
#在cmd中啓動MySQL並將密碼修改爲123456
mydb = mysql.connector.connect(
    host='localhost',
    user='root',
    passwd='123456',
    database='mydatabase',
    buffered = True
)
print(mydb)
#1、創建數據庫
mycursor = mydb.cursor()
# mycursor.execute("CREATE DATABASE mydatabase") #已創建的數據庫再創建會報錯
# mycursor.execute("CREATE DATABASE yangdatabase")


#/*tableName:爲要查詢的表，selSql爲查詢語句，val爲要查詢的where條件中的值***/
def selectFn(mycursor,tableName,selSql,val):
    if selSql=="":
        selSql="select * from "+tableName
        mycursor.execute(str(selSql))
    elif val!="":
        mycursor.execute(str(selSql),val)
    elif val=="":
        mycursor.execute(str(selSql))

    myRes = mycursor.fetchall()
    print(tableName," 表中數據有：")
    for x in myRes:
        print(x)

#/*tableName:爲要插入值的表名，colStr爲表中的字段，valList爲要插入的值***/
def insertFn(mycursor,tableName,colStr,valList):
    #插入的SQL語句：insert into customers(name,address) values(%s,%s)
    splitStr = colStr.split(",")
    valStr=""
    #如下for循環是生成(%s,%s)
    for x in range(len(splitStr)):
        valStr+="%s"
        if (x == (len(splitStr)-1)):
            break
        valStr += ","
    insertSql = "insert into " + tableName + "(" + colStr + ")" +" values(" + valStr + ")"
    mycursor.executemany(str(insertSql),valList)
    mydb.commit()
    print(mycursor.rowcount, " record inserted")
    # print("1 record inserted,ID:", mycursor.lastrowid)


# select出重複數據並刪除
def deleteSameData(delSql,tableName):
    mycursor.execute(delSql)
    mycursor.execute(str("select * from " +tableName))
    myresult1 = mycursor.fetchall()
    for x in myresult1:
        print(x)


#1、檢查數據庫是否創建好
print("1、檢查數據庫是否創建好")
mycursor.execute("SHOW DATABASES")
for x in mycursor:
     print(x)

#2、創建表
mycursor.execute("drop table if exists users")
mycursor.execute("drop table if exists products")
createSql="create table if not exists users(name varchar(255),fav int)"
createSql2="create table if not exists products(id int,name varchar(255))"
valUsers = [
    ('John', 154),
    ('Peter', 154),
    ('Amy', 155),
    ('Hannah', 0),
    ('Michael', 0)
]
valProducts=[
    (154, 'Chocolate Heaven'),
    (155, 'Tasty Lemons'),
    (156, 'Vanilla Dreams'),
    (159, 'yang Cake')
]

mycursor.execute(createSql)
mycursor.execute(createSql2)
mydb.commit()


#3、開始對錶插入數據
print("3、開始對錶插入數據")
insertFn(mycursor,'users','name,fav',valUsers)
insertFn(mycursor,'products','id,name',valProducts)
mycursor.execute("alter  table users add column uid int auto_increment primary key")


#4、查詢表中的數據
print("4、查詢表中的數據")
selectFn(mycursor,'users','','')
selectFn(mycursor,'products','','')


sql2 = "SELECT * FROM customers WHERE address = %s"
adr=("Yellow Garden 2", )
selectFn(mycursor,'customers',sql2,adr)



#5、練習join相關sql語句
print("5、練習join相關sql語句：")
joinSql ="select users.name as user,products.name as favor from users inner join products on users.fav = products.id"
# mycursor.execute(selectSql)
# # selectRes=mycursor.fetchall()
# # for x in selectRes:
# #     print(x)
selectFn(mycursor,'users',joinSql,'')

leftJoinSql ="select users.name as user,products.name as favor from users left join products on users.fav = products.id"
rightJoinSql ="select users.name as user,products.name as favor from users right join products on users.fav = products.id"
selectFn(mycursor,'users',leftJoinSql,'')
selectFn(mycursor,'users',rightJoinSql,'')

join或inner join (例子：組合用戶和產品，查看用戶最喜歡的產品名稱)
組合兩張或更多表
您可以使用 JOIN 語句，根據它們之間的相關列組合兩個或多個表中的行

LEFT JOIN（例子：選擇所有用戶及其喜愛的產品）
在上例中，Hannah 和 Michael 被排除在結果之外，這是因爲 INNER JOIN 只顯示匹配的記錄。
如果希望顯示所有用戶，即使他們沒有喜歡的產品，請使用 LEFT JOIN 語句；

RIGHT JOIN（例子：選擇所有產品以及喜歡它們的用戶）
如果您想要返回所有產品以及喜歡它們的用戶，即使沒有用戶喜歡這些產品，請使用 RIGHT JOIN 語句：

執行結果：

1、檢查數據庫是否創建好
    ('mydatabase',)
    ('mysql',)
    ('yangdatabase',)
3、開始對錶插入數據
       5  record inserted
      4  record inserted
4、查詢表中的數據

users  表中數據有：
('John', 154, 1)
('Peter', 154, 2)
('Amy', 155, 3)
('Hannah', 0, 4)
('Michael', 0, 5)

products  表中數據有：
(154, 'Chocolate Heaven')
(155, 'Tasty Lemons')
(156, 'Vanilla Dreams')
(159, 'yang Cake')

customers  表中數據有：
('Vicky', 'Yellow Garden 2', 11)
5、練習join相關sql語句：

組合用戶和產品，查看用戶最喜歡的產品名稱：
('John', 'Chocolate Heaven')
('Peter', 'Chocolate Heaven')
('Amy', 'Tasty Lemons')

選擇所有用戶及其喜愛的產品：
('John', 'Chocolate Heaven')
('Peter', 'Chocolate Heaven')
('Amy', 'Tasty Lemons')
('Hannah', None)
('Michael', None)

選擇所有產品以及喜歡它們的用戶：
('John', 'Chocolate Heaven')
('Peter', 'Chocolate Heaven')
('Amy', 'Tasty Lemons')
(None, 'Vanilla Dreams')
(None, 'yang Cake')