Effective Techniques for Filtering Data by Time in PostgreSQL

PostgreSQL stores timestamps with high precision, including date, time, and optionally, time zone information. There are two main timestamp data types:

• TIMESTAMP: Stores date and time without a time zone.
• TIMESTAMPTZ: Stores date, time, and time zone information.

Comparing Timestamps in WHERE Clause

You can compare timestamps in the WHERE clause using standard comparison operators like:

• = (equal to)
• < (less than)
• > (greater than)
• <= (less than or equal to)

There are two main ways to specify timestamps for comparison:

Additional Considerations

Here are some examples:

-- Select rows where timestamp_col is after July 6th, 2024
SELECT * FROM my_table WHERE timestamp_col > '2024-07-06';

-- Select rows where another_timestamp_col is within the last hour (assuming timestamp is in UTC)
SELECT * FROM my_table WHERE another_timestamp_col >= current_timestamp - interval '1 hour';

Example Codes for Comparing Timestamps in PostgreSQL WHERE Clause

Comparing with Timestamp Literal:

This example selects rows from the "orders" table where the "created_at" timestamp is equal to July 4th, 2024 (assuming timestamp is without time zone):

SELECT * FROM orders
WHERE created_at = '2024-07-04';

Comparing with a Variable:

This example assumes you have a variable @recent_time set to a specific timestamp. It selects orders created after that time:

SELECT * FROM orders
WHERE created_at > @recent_time;

Comparing with another Column:

This example finds orders where the "shipped_at" timestamp is later than the "created_at" timestamp for the same order:

SELECT * FROM orders
WHERE shipped_at > created_at;

Comparing with a Date Literal (Implicit Conversion):

This example selects orders created on or after July 1st, 2024 (assuming "created_at" is a timestamp). PostgreSQL treats the date literal as a timestamp with '00:00:00' time:

SELECT * FROM orders
WHERE created_at >= '2024-07-01';

Comparing timestamps with Time Zone Awareness (assuming TIMESTAMPTZ data type):

This example selects orders placed in the UTC time zone within the last day:

SELECT * FROM orders
WHERE order_time AT TIME ZONE 'UTC' >= current_timestamp AT TIME ZONE 'UTC' - interval '1 day';

Instead of directly comparing timestamps, you can extract specific parts (year, month, day, hour, etc.) using functions like date_part(), extract(), and compare those values. This can be useful for filtering based on specific time components.

Example:

-- Select orders placed in June 2024
SELECT * FROM orders
WHERE date_part('year', created_at) = 2024 AND date_part('month', created_at) = 6;

Using INTERVAL Arithmetic:

You can leverage the INTERVAL data type to represent a duration and perform arithmetic on timestamps. This helps compare timestamps based on relative time differences.

-- Select orders placed within the last 2 hours (assuming timestamp is in UTC)
SELECT * FROM orders
WHERE created_at >= current_timestamp - interval '2 hour';

BETWEEN Operator for Ranges:

The BETWEEN operator allows you to specify a range of timestamps for comparison. This is useful for filtering data within a specific time window.

-- Select orders placed between July 5th, 2024 (10:00 AM) and July 6th, 2024 (5:00 PM)
SELECT * FROM orders
WHERE created_at BETWEEN '2024-07-05 10:00:00' AND '2024-07-06 17:00:00';

CASE Expressions for Conditional Comparisons:

You can use CASE expressions to perform conditional logic based on timestamp comparisons. This allows for more complex filtering criteria.

-- Select orders marked as urgent if created within the last hour
SELECT *,
  CASE WHEN created_at >= current_timestamp - interval '1 hour' THEN 'Urgent' ELSE 'Normal' END AS urgency
FROM orders;