Retrieving Rows Between Two Dates in PostgreSQL

PostgreSQL provides several ways to retrieve rows that fall within a specific date range. In this article, we will explore one such approach using the date data type and its various operators.

Introduction to Date Data Type

The date data type is used to represent dates without time components. This data type is useful when you need to store or compare dates without considering their time parts. PostgreSQL provides several functions and operators for manipulating date values, including comparisons.

Problem Statement

Suppose you have a table with the following structure:

ID        START_DATE        END_DATE

1         02/03/2020       02/03/2021

2         05/04/2020       NULL

You want to retrieve rows where the date falls between START_DATE and END_DATE. Note that the END_DATE column is nullable.

Solution Approach

One way to approach this problem is by using date operators provided by PostgreSQL. We will use these operators to compare the input date with the START_DATE and END_DATE columns.

Date Operators

PostgreSQL provides several operators for comparing dates, including:

• <=> (comparison): Compares two values element-wise.
• < (less than): Returns TRUE if the first value is less than the second.
• > (greater than): Returns TRUE if the first value is greater than the second.
• <= (less than or equal to): Returns TRUE if the first value is less than or equal to the second.
• >= (greater than or equal to): Returns TRUE if the first value is greater than or equal to the second.

We will use these operators to compare the input date with the START_DATE and END_DATE columns.

Solution

One possible solution using the above operators is:

SELECT *
FROM table_name
WHERE date >= start_date AND (date < end_date OR end_date IS NULL);

In this query, we use the following logic:

• The subquery (date < end_date OR end_date IS NULL) checks if end_date is either less than the input date or if it is null. This ensures that null dates are treated as infinite.

Note that this solution uses a logical AND (AND) operation to combine two conditions: the main condition and the subquery. The main condition checks if the date column falls within the desired range, while the subquery handles the case where end_date is null.

Handling Infinite Dates

When using PostgreSQL’s date data type, you can treat infinite dates by using a specific value, such as infinity (infinity) or negative infinity (-infinity). This allows you to compare these values with other dates in your query.

For example:

SELECT *
FROM table_name
WHERE date > start_date AND (date < end_date OR end_date IS NULL);

In this modified solution, we use the >=' operator to check if the date column is greater than or equal to start_date. This ensures that infinite dates are treated as starting points.

Example Use Case

Suppose you have a table with customer data and want to retrieve customers who made purchases between January 1st, 2020, and December 31st, 2022:

CREATE TABLE orders (
    id INT,
    date DATE,
    amount DECIMAL(10, 2)
);

INSERT INTO orders (id, date, amount) VALUES
(1, '01/01/2020', 100.00),
(2, '12/31/2020', 200.00),
(3, '01/01/2021', NULL);

You can use the following query to retrieve the orders between January 1st, 2020, and December 31st, 2022:

SELECT *
FROM orders
WHERE date >= '01/01/2020' AND (date < '12/31/2022' OR '12/31/2022' IS NULL);

This query returns the following result set:

Note that order #2 is included in the results even though its date is null because it falls within the desired date range.

Conclusion

In this article, we explored one approach to retrieve rows between two dates in PostgreSQL using the date data type and various operators. We used logical AND (AND) operations to combine conditions and treated infinite dates by using specific values like infinity (infinity).

Last modified on 2023-09-26