If you need to add or subtract a time interval from a date in SQL Server, DATEADD() is the function you want. It’s straightforward to use, works with a wide range of date parts, and covers most date arithmetic you’ll ever need.
dates
Fix Error 155 “‘DAYS’ is not a recognized dateadd option” in SQL Server
If you’re getting an error that reads something like “‘DAYS’ is not a recognized dateadd option” in SQL Server, it’s because you’re using the DATEADD() function with an invalid datepart argument.
This often happens when you use a plural form of the argument. For example, DAYS instead of DAY. Or HOURS instead of HOUR.
The easiest way to fix this is to provide a valid datepart argument.
How to Get the Current Date in SQL Server
SQL Server has several functions that return the current date and time. If you just need today’s date for a query, that sounds like it should be simple. And it is. But there are six different functions to choose from, and they don’t all return the same thing. This article explains what each one does and when to use it.
Fix “The datepart … is not supported by date function dateadd for data type date” in SQL Server
If you’re getting error 9810 that reads something like “The datepart hour is not supported by date function dateadd for data type date“, it’s because the datepart that you’re trying to add or subtract a datepart is not supported for the data type of the original value.
This typically happens when you try to add a timepart to a date value. For example, trying to add an hour to a date value will result in this error, because the date type doesn’t support the hour datepart. You can’t have a date value that includes the hour.
How to Format Dates in SQL Server (A Beginner’s Guide)
Dates in SQL Server can be surprisingly tricky if you’re new to the game. The way dates are stored is not always the way you want them displayed, and figuring out how to convert one to the other is one of those things every beginner eventually Googles. So let’s walk through it clearly.
Using Multiple Window Calculations with DATEDIFF() in SQL Server
SQL Server’s window functions allow you to perform calculations across sets of rows that are related to the current row, without collapsing those rows into a single result like traditional GROUP BY aggregates would. When combined with the DATEDIFF() function, they provide a great way to analyze temporal patterns in your data.
Window functions can be especially useful when you need to perform multiple different calculations across the same dataset. Instead of writing separate subqueries or self-joins for each calculation, you can combine multiple window expressions in a single query. This approach is cleaner, more maintainable, and often more performant than traditional alternatives.
Using Subqueries with SQL Server’s DATEDIFF() Function
While SQL Server’s DATEDIFF() function is relatively straightforward when you’re comparing two known dates, it becomes more flexible when the dates you compare are sourced directly from your tables. Instead of hardcoding dates, you can embed subqueries directly into the DATEDIFF() function to dynamically retrieve the dates you need.
This approach can be especially useful when you’re working with aggregate functions like MIN() and MAX(), or when you need to pull specific dates based on certain conditions. The subqueries execute first, return their date values, and DATEDIFF() uses those results to perform the calculation.
Calculating Days Between a Fixed Date and Dynamic Dates with DATEDIFF()
Sometimes you need to measure how many days have passed between a specific reference point and a constantly moving target. SQL Server’s DATEDIFF() function handles this elegantly by letting you combine hardcoded dates with dynamic functions like GETDATE(). This can be useful for calculating things like age, days since an event, or time remaining until a deadline.
The main point here is that DATEDIFF() doesn’t care whether its date arguments are literals, functions, or even subqueries. It just needs two date values to compare. When you use GETDATE() or similar functions, you’re telling SQL Server to calculate the difference based on the current moment, which means the result changes every time you run the query.
Using DATEDIFF() with LEAD() to Calculate Time Until Future Events
When you’re analyzing how events unfold over time in a SQL database, one of the biggest challenges can be efficiently comparing what’s happening now to what comes next. Each event typically appears as its own row with a timestamp, but meaningful insight often comes from understanding how those timestamps relate to one another. Fortunately SQL Server provides some useful tools for this kind of sequential analysis.
Rather than relying on bulky self-joins or multi-step logic, SQL window functions offer a streamlined way to track these transitions. For example, by pairing the LEAD() function with DATEDIFF(), you can instantly measure the gap between consecutive events and surface insights that would otherwise require far more complex queries.
Generating Staggered Dates with SQL Server Window Functions
SQL Server’s window functions open up some creative possibilities when you need to work with dates. One interesting pattern involves pairing DATEADD() with ROW_NUMBER() to automatically generate sequential dates based on your query results.
This technique gives you a flexible way to calculate dates dynamically without hardcoding values or maintaining separate date tables. This can be useful for doing things like building a scheduling system, creating test data with realistic timestamps, or just spacing events across a timeline.