Press "Enter" to skip to content

Category: Dates and Numbers

Adding a UTC Time Zone Indicator to a Date in SQL Server

Published 2023-05-04 by Kevin Feasel

Bill Fellows fights with the language:

It seems so easy, I was building json in SQL Server and the date format for the API specified it needed to have 3 millsecond digits and the zulu timezone signifier. Easy peasy, lemon squeezey, that is ISO8601 with time zone Z format code 127

SELECT CONVERT(char(24), GETDATE(), 127) AS waitAMinute; Running that query yields something like 2023-05-02T10:47:18.850 Almost there but where’s my Z? Hmmm, maybe it’s because I need to put this into UTC? SELECT CONVERT(char(24), GETUTCDATE(), 127) AS SwingAndAMiss;

Running that query yields something like 2023-05-02T15:47:18.850 It’s in UTC but still no timezone indicator.

Read on for several attempts and what finally did the trick.

Comments closed

Rounding Errors by Data Type in DAX

Published 2023-04-25 by Kevin Feasel

Marco Russo and Alberto Ferrari shave of fractions of a cent:

The first reason to choose a data type is the range of numbers supported and the precision. However, the result of a mathematical operation may produce a number that cannot be represented in the chosen data type, which requires a rounding operation. Therefore, the result of one same sequence of operations can produce different results depending on the data type and the order of execution. In this article, we discuss the typical rounding behavior for each data type and how to avoid possible issues in your DAX formulas because of any differences from the results you may have expected.

Read on to learn what granularity limits exist for integers, fixed decimal numbers, and floating point operations.

Comments closed

Building a Time Dimension in Power BI

Published 2023-04-07 by Kevin Feasel

Allison Kennedy shares a variant of DimTime:

 Today’s post is going to be short and sweet. I’m simply publishing my version of a DimTime table for Power BI.

Thanks to Radacad for posting a great article on why we need a DimTime table, along with their script for creating one in Power BI. 

If you don’t already have a DimDate table, you can find my version in my DimDate: What, Why and How blog article. I update the script occasionally with new requests. 

Click through for the script.

Comments closed

End of Month in Snowflake and SQL Server

Published 2023-03-15 by Kevin Feasel

Kevin Wilkie is ready for that end-of-month paycheck:

When you work with data, you’ll probably need to work with dates at least once a month. That is the nature of the beast. Today, let’s compare working with them in SQL Server and Snowflake. I want to focus only on adding and subtracting months when provided with a specific day.

Along the way, I would also push for a calendar table, so that you can remove some of the more difficult (or even most common) date calculations.

Comments closed

Fun with Implicit Conversions to DateTime

Published 2023-03-01 by Kevin Feasel

Andrea Allred gets tested:

I have been teaching a T-SQL 101 class and for the homework, we asked the students to get all the records where our heroes had a birthdate between 1995 through 1999. I expected something like this:

[…]

Imagine my surprise when one of the students turned in this:

SELECT FirstName, LastName, Birthdate
FROM Heroes
WHERE Birthdate BETWEEN '1995' AND '1999'

When I first saw the query I thought, “There is no way they ran that and it worked.” So I wrote it up and ran it on my data. Guess what? IT RUNS AND RETURNS DATA! I was shocked.

Click through to see what it returns and how that’s not quite right.

Comments closed

Building an Event Calendar from T-SQL and CSS

Published 2023-02-22 by Kevin Feasel

Aaron Bertrand builds some HTML:

In my last tip, I showed how to use T-SQL to generate HTML for fancy calendar visuals overlaid with event data from another table. As an extension of that tip, let’s now look at simplifying parts of that query by caching the date information in a calendar table to streamline the outer queries and avoid complications caused by different DATEFIRST settings.

This is the follow-on from a prior post (linked in the lede here), so it would make sense to read that one first if you haven’t already.

Comments closed

Approximation with the Mediant

Published 2023-02-08 by Kevin Feasel

John Cook didn’t make a typo:

Suppose you are trying to approximate some number x and you’ve got it sandwiched between two rational numbers:

a/b < x < c/d.

Now you’d like a better approximation. What would you do?

The obvious approach would be to take the average of a/b and c/d. That’s fine, except it could be a fair amount of work if you’re doing this in your head.

Read on for a separate approach taking the mediant (not median) of the two fractions.

Comments closed

Regionally Formatted Dates in Excel and Power BI

Published 2023-02-02 by Kevin Feasel

Allison Kennedy wrangles dates:

Dates are fundamental to pretty much every report. No matter what industry you work in, at some stage you’re going to work with dates in your reporting. This might be in the form of Semesters, Quarters, Seasons, Weeks, or just good old fashioned Dates. 

If you’re working with Power Query or Power BI, you should have a Date Table. In this post, I’m going to demonstrate how to work with Dates that can be tricky to format. 

Click through for examples of three common challenges when working with dates in Excel and Power BI.

Comments closed

Testing BIGINT Support in Applications

Published 2023-01-04 by Kevin Feasel

Michael J. Swart reminds us that it’s not just the database which needs to be able to handle large values:

In the past I’ve written about monitoring identity columns to ensure there’s room to grow.

But there’s a related danger that’s a little more subtle. Say you have a table whose identity column is an 8-byte bigint. An application that converts those values to a 4-byte integer will not always fail! Those applications will only fail if the value is larger than 2,147,483,647.

This post specifically pertains to identity columns but don’t forget those non-identity columns when testing.

Comments closed

Time Zone Conversion in SQL Server

Published 2022-11-22 by Kevin Feasel

Ed Pollack wants to know what time it is:

Converting a current time from one time zone to another is relatively easy. Regardless of whether daylight savings is involved or not, one simply needs to retrieve the current time in both time zones, find the difference, and apply that difference as needed to date/time calculations. Historical data is trickier, though, as times from the past may cross different daylight savings boundaries.

This article dives into all the math required to convert historical times between time zones. While seemingly academic in nature, this information can be used when building applications that interact between time zones and need to apply detailed rules to those applications and their users. These calculations will be demonstrated in T-SQL and a function built that can help in handling the math for you.

The pro tip is to store all data in UTC and perform date and time calculations at the edge, where you know the user’s time zone. Ed has plenty of good advice in here as well.

Comments closed