Learning PostgreSQL 11 - Third Edition

Reading data from a database

When a query that returns a dataset is executed in a cursor, this data can be made available in the application. This is not only about SELECT queries, but also any data-changing query that has a RETURNING clause.

Suppose there is a cursor that has executed a query, as follows:

cur = conn.cursor()cur.execute("SELECT make, model FROM car_portal_app.car_model")

The cursor object provides several ways to retrieve the data:

• Use the object as an iterator:

for record in cur:    print("Make: {}, model: {}".format(record[0], record[1]))

Here, record is a tuple and the values of the fields can be accessed using the square-bracket syntax, specifying the number of the field (zero-based).

• Invoke the cursor.fetchone() method ...