Python MySQL Dabagaya

组合两张或更多表

您可以使用 JOIN 语句，根据它们之间的相关列组合两个或多个表中的行。

假设您有 "users" 表和 "products" 表：

users

{ id: 1, name: 'John', fav: 154},
{ id: 2, name: 'Peter', fav: 154},
{ id: 3, name: 'Amy', fav: 155},
{ id: 4, name: 'Hannah', fav:},
{ id: 5, name: 'Michael', fav:}

products

{ id: 154, name: 'Chocolate Heaven' },
{ id: 155, name: 'Tasty Lemons' },
{ id: 156, name: 'Vanilla Dreams' }

可以使用 users 的 fav 字段和 products 的 id 字段来组合这两个表。

Mafi

组合用户和产品，查看用户最喜欢的产品名称：

import mysql.connector
mydb = mysql.connector.connect(
  host="localhost",
  user="yourusername",
  passwd="yourpassword",
  database="mydatabase"
)
mycursor = mydb.cursor()
sql = "SELECT \",
  users.name AS user, \
  products.name AS favorite \
  FROM users \
  INNER JOIN products ON users.fav = products.id"
mycursor.execute(sql)
myresult = mycursor.fetchall()
for x in myresult:
  print(x)

Harci Mafi

Rarraba:A yi amfani da JOIN ko INNER JOIN, za a samar da cikakken sakamfuran.

LEFT JOIN

A cikin shaidar da yake, Hannah da Michael sun kama a cikin kudade daga cikin nisha-wan nisha, saboda INNER JOIN yana nuna kudade da su wanzuwa kaiwa.

Idan a baya yin kaiwa da duk mutumtattun, kuma ba a samar da kwallon anya da su kara su a kaiwa ba, ya kamata a yi amfani da jumullar LEFT JOIN:

Mafi

Yana zartarwa duk mutumtattun da kwallon anya su kara su a kaiwa:

sql = "SELECT \",
  users.name AS user, \
  products.name AS favorite \
  FROM users \
  LEFT JOIN products ON users.fav = products.id"

Harci Mafi

RIGHT JOIN

Idan a baya yin kaiwa da duk kwallon anya da mutumtattun da su kara su a kaiwa, kuma ba a samar da mutumtattun da ba su kara su a kaiwa ba, ya kamata a yi amfani da jumullar RIGHT JOIN:

Mafi

sql = "SELECT \",
  users.name AS user, \
  products.name AS favorite \
  FROM users \
  RIGHT JOIN products ON users.fav = products.id"

Harci Mafi

Rarraba:Hannah da Michael, wa su koyi ba su da hauwa da kwallon anya, sun kama a cikin kudade daga cikin nisha-wan nisha.