Memfilter dan menargetkan data

Pengantar Basis Data di Python

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

Klausa where

stmt = select([census])

stmt = stmt.where(census.columns.state == 'California')

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

for result in results:
    print(result.state, result.age)

California 0
California 1
California 2
California 3
California 4
California 5
...

Klausa where

Membatasi data yang dikembalikan kueri berdasarkan kondisi Boolean
Membandingkan kolom dengan nilai atau kolom lain
Sering memakai perbandingan ==, <=, >=, atau !=

Ekspresi

Menyediakan kondisi yang lebih kompleks daripada operator sederhana
Mis. in_(), like(), between()
Banyak lagi di dokumentasi
Tersedia sebagai metode pada Column

Ekspresi

stmt = select([census])

stmt = stmt.where(census.columns.state.startswith('New'))

for result in connection.execute(stmt):
    print(result.state, result.pop2000)

New Jersey 56983
New Jersey 56686
New Jersey 57011
...

Konjungsi

Memungkinkan beberapa kriteria dalam klausa where
Mis. and_(), or_(), not_()

Konjungsi

from sqlalchemy import or_

stmt = select([census])

stmt = stmt.where(
    or_(census.columns.state == 'California',
        census.columns.state == 'New York'
    )
)

for result in connection.execute(stmt):
    print(result.state, result.sex)

New York M
...
California F

Ayo berlatih!

Pengantar Basis Data di Python