Updating data in a table

Introduction to Databases in Python

Jason Myers

Co-Author of Essential SQLAlchemy and Software Engineer

Updating data in a table

Done with the update() statement
Similar to the insert() statement but includes a where clause to determine what record will be updated
We add all the values we want to update with the values() clause as column=value pairs

Updating one row

from sqlalchemy import update

stmt = update(employees)
stmt = stmt.where(employees.columns.id == 3)
stmt = stmt.values(active=True)

result_proxy = connection.execute(stmt)
print(result_proxy.rowcount)

Updating multiple rows

Build a where clause that will select all the records you want to update

Inserting multiple rows

stmt = update(employees)
stmt = stmt.where(employees.columns.active == True)

stmt = stmt.values(active=False, salary=0.00)

result_proxy = connection.execute(stmt)
print(result_proxy.rowcount)

Correlated updates

new_salary = select([employees.columns.salary])
new_salary = new_salary.order_by(
    desc(employees.columns.salary))
new_salary = new_salary.limit(1)

stmt = update(employees)

stmt = stmt.values(salary=new_salary)

result_proxy = connection.execute(stmt)

print(result_proxy.rowcount)

Correlated updates

Uses a select() statement to find the value for the column we are updating
Commonly used to update records to a maximum value or change a string to match an abbreviation from another table

Let's practice!

Introduction to Databases in Python

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