How to Find Overlapping Time Intervals Between Two SQL Tables?

Finding Overlapping Time Intervals between Two Tables in SQL

In a database with two tables containing start and end time fields, it is often necessary to identify rows where the time intervals intersect. This question provides a solution for efficiently finding such overlaps in SQL Server 2005 using a WHERE-clause.

Solution:

The following query can be used to find overlapping time intervals between rows in table1 and table2:

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

Explanation:

The query uses a JOIN condition to compare the time intervals from both tables. The WHERE-clause employs two conditions:

1. table2.start <= table1.end ensures that the start time of row 2 (table2) occurs before or at the same time as the end time of row 1 (table1).
2. (table2.end IS NULL OR table2.end >= table1.start) handles the case where the end time in table2 is NULL or occurs on or after the start time in table1. This condition ensures that overlapping intervals are captured.

This WHERE-clause effectively determines whether the time interval of row 2 intersects with the time interval of row 1. By using a join, the query efficiently retrieves rows from both tables where such overlaps exist.

The above is the detailed content of How to Find Overlapping Time Intervals Between Two SQL Tables?. For more information, please follow other related articles on the PHP Chinese website!