Introduction to SQL queries

Introduction to Databases in Python

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

SQL Statements

Select, insert, update, and delete data
Create and alter data

Basic SQL querying

SELECT column_name FROM table_name

SELECT pop2008 FROM People
SELECT * FROM People

Basic SQL querying

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 is a ResultProxy
results is a ResultSet

Handling ResultSets

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 to build queries

Provides a Pythonic way to build SQL statements
Hides differences between backend database types

SQLAlchemy querying

from sqlalchemy import Table, MetaData
metadata = MetaData()

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

stmt = select([census])

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

SQLAlchemy select statement

Requires a list of one or more Tables or Columns
Using a table will select all the columns in it

stmt = select([census])

print(stmt)

'SELECT * from CENSUS'

Let's practice!

Introduction to Databases in Python