You can get into a situation where you have two tables with values associated with date ranges. What’s worse, those date ranges don’t necessarily have to align, which can make joining them a seemingly complex task, but it is surprisingly simple when you learn how to think of overlapping date ranges, along with this relatively simple T-SQL join pattern.
Tag: interval
Turn your list into human-readable intervals
If you’ve worked with reporting, you’ve probably come across the following problem. You have a list of values, say “A, B, C, D, K, L, M, N, R, S, T, U, Z” that you want to display in a more user-friendly, condensed manner, “A-D, K-N, R-U, Z”.
Today, we’re going to look at how you can accomplish this in T-SQL, and what this has to do with window functions and gaps and islands.
Human-readable ranges of integers or dates
This is a real-world problem that I came across the other day. In a reporting scenario, I wanted to output a number of values in an easy, human-readable way for a report. But just making a long, comma-separated string of numbers doesn’t really make it very readable. This is particularly true when there are hundreds of values.
So here’s a powerful pattern to solve that task.
Joining two SCD2 tables
A number of OLTP systems store dimension data in SCD2-like tables in order to retain all the revisions whenever the dimension information changes. In certain situations, you may come across a need to join two or more SCD tables, while keeping all the versions information intact. Sound tricky? Not really.
Distributing values with overlapping ranges
Today, we’re going to look at how to distribute values with what I call “overlapping ranges”. What I mean by that is that the value that you need to distribute has a given range and the objects you want to distribute the values to are also defined as ranges. Sound complicated? It doesn’t have to.
Working with intervals
At one point or another, you’re going to come across intervals when working in SQL Server. You could say that an interval is where you don’t have a single value, but actually a range of values, commonly delimited within a start and an end value. This range could be a group of accounts, versions of dimension members (in an SCD) or date/time intervals.
A function to parse ranges
Here’s a quick function to parse a list of ranges (in a varchar variable) into a table of ranges. Might come in practical, for instance when parsing user arguments for a report.