Pengantar kueri SQL

Pengantar Basis Data di Python

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

Pernyataan SQL

Select, insert, update, dan delete data
Membuat dan mengubah data

Kueri SQL dasar

SELECT column_name FROM table_name

SELECT pop2008 FROM People
SELECT * FROM People

Kueri SQL dasar

from sqlalchemy import create_engine

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

connection = engine.connect()

stmt = 'SELECT * FROM people'

result_proxy = connection.execute(stmt)

results = result_proxy.fetchall()

ResultProxy vs ResultSet

result_proxy = connection.execute(stmt)

results = result_proxy.fetchall()

result_proxy adalah ResultProxy
results adalah ResultSet

Mengelola ResultSet

first_row = results[0]
print(first_row)

('Illinois', 'M', 0, 89600, 95012)

print(first_row.keys())

['state', 'sex', 'age', 'pop2000', 'pop2008']

print(first_row.state)

'Illinois'

SQLAlchemy untuk membangun kueri

Cara bergaya Python untuk membangun pernyataan SQL
Menyamarkan perbedaan antar jenis basis data backend

Kueri dengan SQLAlchemy

from sqlalchemy import Table, MetaData
metadata = MetaData()

census = Table('census', metadata, autoload=True,
  autoload_with=engine)

stmt = select([census])

results = connection.execute(stmt).fetchall()

Pernyataan select di SQLAlchemy

Memerlukan daftar satu atau lebih Table atau Column
Menggunakan sebuah tabel akan memilih semua kolom di dalamnya

stmt = select([census])

print(stmt)

'SELECT * from CENSUS'

Ayo berlatih!

Pengantar Basis Data di Python