Extending PostgreSQL

Functions for Manipulating Data in PostgreSQL

Brian Piccolo

Sr. Director, Digital Strategy

User-defined data types

Enumerated data types

CREATE TYPE dayofweek AS ENUM (
      'Monday', 
      'Tuesday',
      'Wednesday', 
      'Thursday', 
      'Friday', 
      'Saturday', 
      'Sunday'
);

Getting information about user-defined data types

SELECT typname, typcategory
FROM pg_type
WHERE typname='dayofweek';

+-----------+-------------+
| typname   | typcategory |
|-----------|-------------|
| dayofweek | E           |
+-----------+-------------+

Getting information about user-defined data types

SELECT column_name, data_type, udt_name
FROM INFORMATION_SCHEMA.COLUMNS 
WHERE table_name ='film';

+-----------------------------------------------+
| column_name | data_type         | udt_name    |
|-------------|-------------------|-------------|
| title       | character varying | varchar     |
| rating      | USER-DEFINED      | mpaa_rating |
+-----------------------------------------------+

User-defined functions

CREATE FUNCTION squared(i integer) RETURNS integer AS $$
    BEGIN
        RETURN i * i;
    END;
$$ LANGUAGE plpgsql;

SELECT squared(10);

+---------+
| squared |
|---------|
| 100     |
+---------+

User-defined functions in the Sakila database

get_customer_balance(customer_id, effective_data): calculates the current outstanding balance for a given customer.
inventory_held_by_customer(inventory_id): returns the customer_id that is currently renting an inventory item or null if it's currently available.

inventory_in_stock(inventory_id): returns a boolean value of whether an inventory item is currently in stock.

Let's practice!

Functions for Manipulating Data in PostgreSQL