Mastering Postgresql: Merge Overlapping Ranges Only and Ignore Adjacent

Are you tired of dealing with pesky overlapping ranges in your Postgresql database? Do you find yourself tangled in a web of confusing queries and inefficient solutions? Fear not, dear reader, for today we’re going to dive into the wonderful world of range merging and explore the amazing technique of merging overlapping ranges only and ignoring adjacent ones.

What is Range Merging and Why Do We Need It?

Range merging is the process of combining multiple ranges into a single, cohesive range. This is particularly useful in scenarios where you have multiple overlapping or adjacent ranges that need to be consolidated. For instance, suppose you have a table that stores employee work schedules, with each row representing a specific date range. If an employee has multiple rows with overlapping dates, you’d want to merge those ranges to get a clear picture of their overall work schedule.

But why do we need range merging? Well, having multiple overlapping ranges can lead to:

• Inconsistent data: Overlapping ranges can cause data inconsistencies, making it difficult to analyze or query the data accurately.
• Performance issues: Querying multiple overlapping ranges can result in slower performance, especially with large datasets.
• Difficulty in analysis: With multiple overlapping ranges, it’s challenging to get a clear understanding of the overall trend or pattern.

The Problem with Adjacent Ranges

When working with range merging, adjacent ranges can be a major hurdle. Adjacent ranges are ranges that don’t overlap but are consecutive. For example:

| Range    | 
|---------|
| [1, 5)  |
| [5, 10) |

In the above example, the two ranges are adjacent, meaning they don’t overlap but are consecutive. If we simply merge these ranges, we’d get:

| Range    | 
|---------|
| [1, 10) |

However, this might not always be the desired outcome. In some cases, we might want to ignore adjacent ranges and only merge overlapping ones. This is where the “merge overlapping range only and ignore adjacent” technique comes into play.

The Magic of Postgresql’s Range Functions

Postgresql provides an array of range functions that can be used to manipulate and merge ranges. The two most relevant functions for our purpose are:

• range_merge(): Merges multiple ranges into a single range.
• range_overlap(): Returns true if two ranges overlap, false otherwise.

Using these functions, we can create a query that merges overlapping ranges only and ignores adjacent ones.

The Solution: Merging Overlapping Ranges Only

Here’s an example query that demonstrates the technique:

WITH ranges AS (
  SELECT '[1, 5)'::int4range AS range_val UNION ALL
  SELECT '[3, 7)' UNION ALL
  SELECT '[5, 10)' UNION ALL
  SELECT '[8, 12)'
)
SELECT range_merge(r1.range_val)
FROM ranges r1
WHERE NOT EXISTS (
  SELECT 1
  FROM ranges r2
  WHERE r2.range_val && r1.range_val
  AND range_lower(r2.range_val) = range_upper(r1.range_val) - 1
  OR range_upper(r2.range_val) = range_lower(r1.range_val) + 1
);

Let’s break down this query:

• We create a Common Table Expression (CTE) named “ranges” that contains our sample ranges.
• We use the range_merge() function to merge the ranges.
• The subquery filters out adjacent ranges by checking if there exists a range that overlaps with the current range and has an upper or lower bound that is one unit away from the current range’s upper or lower bound.
• The NOT EXISTS clause ensures that only ranges that don’t have an adjacent range are merged.

The resulting merged ranges will only contain overlapping ranges, ignoring adjacent ones:

| Range    | 
|---------|
| [1, 7)  |
| [8, 12) |

Handling Edge Cases and Exceptions

When working with range merging, it’s essential to consider edge cases and exceptions. Here are a few scenarios to keep in mind:

Edge Case 1: Empty Ranges

Empty ranges can cause issues with range merging. To handle this, you can add a simple check to ignore empty ranges:

WHERE range_val IS NOT EMPTY

Edge Case 2: Infinite Ranges

Infinite ranges can also cause problems. To handle this, you can add a check to ignore infinite ranges:

WHERE range_upper(range_val) IS NOT NULL
AND range_lower(range_val) IS NOT NULL

Edge Case 3: NULL Ranges

WHERE range_val IS NOT NULL