Azure-Sql-Db

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Administration Level: Medium

Question:

You are trying to truncate a table but the command is failing.

Can you give some examples of what can cause a truncate command on a table to fail?

Answer:

One common reason is that the table is referenced by a FOREIGN KEY constraint. (But you can truncate a table that has a foreign key that references itself).

2025-10-31

We spend a lot of time doing performance tuning work for clients. Inappropriate indexing strategy is often high on the list of issues that we identify. Most of these issues can’t be fixed by SQL Server itself and require a detailed understanding of both how the tables are structured and how they are accessed.

However, there is one very common problem however that I believe SQL Server could assist with.

2025-10-21

This is the eleventh tale in a series of stories about data. I hope you enjoy the series.

Recently, I’ve written a series of articles on how the overall size of a financial services database was tamed by the application of table compression, XML compression, and PDF size reduction. I have applied this approach at many sites but recently came across one where the outcome seemed to constantly be getting worse rather than better. Every time I tried to improve the situation, it got worse. Let’s discuss why.

2025-10-13

This is the tenth tale in a series of stories about data. I hope you enjoy the series.

I regularly see code that calculates a count of a set of rows then makes a decision that’s based on the count, but only on whether or not the count is zero. Consider this (slightly contrived) example based on AdventureWorks:

DECLARE @PersonCount int;

SELECT @PersonCount = COUNT(*)
FROM Person.Password
WHERE BusinessEntityID = 12
AND PasswordHash = 0x208394209302;

IF @PersonCount > 0
BEGIN
    PRINT N'Password matches';
END;

Now I’ll start by saying that the last thing I’d ever want to see in SQL Server code is this sort of playing around with users and passwords, but I’m ignoring that for now.

2025-10-09

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

You are reviewing your development standards and notice that there is a warning about making sure you don’t nest views.

Why would this be an issue?

Answer:

Nested views hide complexity, and worse, the SQL Server optimizer might not be able to eliminate all the tables from the query that it could otherwise have done. This can lead to serious performance issues that could have been avoided.

2025-10-07

This is the ninth tale in a series of stories about data. I hope you enjoy the series.

In the first article we saw why size really does matter, both for the DB itself and all the other copies of it that exist in most organizations. We then saw how to estimate the improvement in size with ROW compression. Our customer’s database that started at 3.8TB was reduced to 2.6TB by applying ROW compression without any code changes. Better still the performance of the I/O bound application improved significantly by compressing the tables and indexes.

2025-10-05

This is the eighth tale in a series of stories about data. I hope you enjoy the series.

In the first article we saw why size really does matter, both for the DB itself and all the other copies of it that exist in most organizations. We then saw how to estimate the improvement in size with ROW compression. Our customer’s database that started at 3.8TB was reduced to 2.6TB by applying ROW compression without any code changes. Better still the performance of the I/O bound application improved significantly by compressing the tables and indexes.

2025-10-01

Just a heads-up that v26 of SDU Tools went out to SDU Insiders last week. If you haven’t used SDU Tools, they are just a large library of functions implemented in T-SQL. You can use them as a full library or use them as examples of code in work you are trying to do.

Fabric SQL Database Release

The main reason for this release (apart from the standard list updates for SQL Server versions, etc.) is to introduce a new target for SDU Tools. When you download v26, you’ll notice there are now three installation scripts, and three removal scripts. So, there are now versions for:

2025-09-30

This is a post in the SQL Interview series. These aren’t trick or gotcha questions, they’re just questions designed to scope out a candidate’s knowledge around SQL Server and Azure SQL Database.

Section: Development Level: Medium

Question:

You regularly execute the following query:

SELECT ProductID,
       UnitPrice / OuterPrice AS PriceRatio
FROM dbo.Products;

When OuterPrice is zero, an error is returned. What is the simplest way to change the query to return NULL for PriceRatio if OuterPrice is zero, without wrapping the expression in a CASE statement?

2025-09-29

This is the seventh tale in a series of stories about data. I hope you enjoy the series.

In the previous article I started discussing a large customer database that needed to go on a diet. We needed to drastically reduce the size of the database. I described why ROW compression was important, and showed how to estimate the savings from using it.

This month, we’ll start by looking at how ROW compression actually works, then look at the greater savings from PAGE compression. We’ll also look at how it works internally.

2025-09-27