Extracting and transforming date / time data

Functions for Manipulating Data in PostgreSQL

Brian Piccolo

Sr. Director, Digital Strategy

Extracting and transforming date and time data

Exploring the EXTRACT(), DATE_PART() and DATE_TRUNC() functions

Transactional timestamp precision not useful for analysis

2005-05-13 08:53:53

Often need to extract parts of timestamps

2005 or 5 or 2 or Friday

Or convert / truncate timestamp precision to standardize

2005-05-13 00:00:00

Extracting and transforming date / time data

EXTRACT( field FROM source )

SELECT EXTRACT(quarter FROM timestamp '2005-01-24 05:12:00') AS quarter;

DATE_PART('field', source)

SELECT DATE_PART('quarter', timestamp '2005-01-24 05:12:00') AS quarter;

+---------+
| quarter |
|---------|
| 1       |
+---------+

Extracting sub-fields from timestamp data

Transactional data from DVD Rentals payment table

SELECT * FROM payment;

+--------------------------------------------------------------------------------+
| payment_id | customer_id | staff_id | rental_id | amount | payment_date        |
|------------|-------------|----------|-----------|--------|---------------------|
| 1          | 1           | 1        | 76        | 2.99   | 2005-05-25 11:30:37 |
| 2          | 1           | 1        | 573       | 0.99   | 2005-05-28 10:35:23 |
| 3          | 1           | 1        | 1185      | 5.99   | 2005-06-15 0:54:12  |
+--------------------------------------------------------------------------------+

Extracting sub-fields from timestamp data

Data from payment table by year and quarter

SELECT 
  EXTRACT(quarter FROM payment_date) AS quarter,
  EXTRACT(year FROM payment_date) AS year, 
  SUM(amount) AS total_payments 
FROM 
  payment 
GROUP BY 1, 2;

Results

+---------------------------------+
| quarter | year | total_payments |
|---------|------|----------------|
| 2       | 2005 | 14456.31       |
| 3       | 2005 | 52446.02       |
| 1       | 2006 | 514.18         |
+---------------------------------+

Truncating timestamps using DATE_TRUNC()

The DATE_TRUNC() function will truncate timestamp or interval data types.

Truncate timestamp '2005-05-21 15:30:30' by year

SELECT DATE_TRUNC('year', TIMESTAMP '2005-05-21 15:30:30');

Result: 2005-01-01 00:00:00

Truncate timestamp '2005-05-21 15:30:30' by month

SELECT DATE_TRUNC('month', TIMESTAMP '2005-05-21 15:30:30');

Result: 2005-05-01 00:00:00

Let's practice!

Functions for Manipulating Data in PostgreSQL