在 Python 中查詢關聯式資料庫

Python 資料匯入入門

Hugo Bowne-Anderson

Data Scientist at DataCamp

基本 SQL 查詢

SELECT * FROM Table_Name

回傳該資料表{{2}}所有列的所有欄
範例：

SELECT * FROM Orders

我們會用 SQLAlchemy 與 pandas

SQL 查詢工作流程

匯入套件與函式
建立資料庫引擎
連線至引擎
查詢資料庫
將查詢結果存成 DataFrame
關閉連線

你的第一個 SQL 查詢

from sqlalchemy import create_engine
import pandas as pd

engine = create_engine('sqlite:///Northwind.sqlite')

con = engine.connect()

rs = con.execute("SELECT * FROM Orders")

df = pd.DataFrame(rs.fetchall())

con.close()

印出查詢結果

print(df.head())

       0      1   2                      3                      4 
0  10248  VINET   5   7/4/1996 12:00:00 AM   8/1/1996 12:00:00 AM   
1  10251  VICTE   3   7/8/1996 12:00:00 AM   8/5/1996 12:00:00 AM   
2  10254  CHOPS   5  7/11/1996 12:00:00 AM   8/8/1996 12:00:00 AM   
3  10256  WELLI   3  7/15/1996 12:00:00 AM  8/12/1996 12:00:00 AM   
4  10258  ERNSH   1  7/17/1996 12:00:00 AM  8/14/1996 12:00:00 AM

設定 DataFrame 欄名

from sqlalchemy import create_engine
import pandas as pd
engine = create_engine('sqlite:///Northwind.sqlite')
con = engine.connect()
rs = con.execute("SELECT * FROM Orders")
df = pd.DataFrame(rs.fetchall())
df.columns = rs.keys()
con.close()

設定資料框欄名

print(df.head())

   OrderID CustomerID  EmployeeID              OrderDate  
0    10248      VINET           5   7/4/1996 12:00:00 AM   
1    10251      VICTE           3   7/8/1996 12:00:00 AM   
2    10254      CHOPS           5  7/11/1996 12:00:00 AM   
3    10256      WELLI           3  7/15/1996 12:00:00 AM   
4    10258      ERNSH           1  7/17/1996 12:00:00 AM

使用內容管理器

from sqlalchemy import create_engine
import pandas as pd
engine = create_engine('sqlite:///Northwind.sqlite')

with engine.connect() as con:
    rs = con.execute("SELECT OrderID, OrderDate, ShipName FROM Orders")
    df = pd.DataFrame(rs.fetchmany(size=5))
    df.columns = rs.keys()

一起來練習吧！

Python 資料匯入入門