How Can SQL Efficiently Identify Overlapping Time Intervals Between Two Tables?

Efficiently Identifying Time-Interval Overlaps in SQL

Problem:

Given two tables with start and end time columns, the task is to identify rows in the second table that overlap in time intervals with each row in the first table. The condition also considers rows in the second table with null end times.

Solution:

Using SQL Server 2005 syntax, the following WHERE-clause effectively addresses this problem:

SELECT * 
FROM table1,table2 
WHERE table2.start <= table1.end 
AND (table2.end IS NULL OR table2.end >= table1.start)

Explanation:

• The clause table2.start <= table1.end ensures that the start time of any potential overlapping interval in table2 is within the end time of the current interval in table1.
• The second condition, table2.end IS NULL OR table2.end >= table1.start, handles null end times in table2. If the end time is null, it is considered to indefinitely extend the interval, potentially overlapping with any subsequent interval in table1. Alternatively, if the end time is a valid value and it is greater than or equal to the start time of the current interval in table1, an overlap is detected.

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