Azure-Sql-Db

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

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 execute the following code:

DROP TABLE IF EXISTS dbo.Table1;
GO

CREATE TABLE dbo.Table1
(
    Column1 int NULL
);
GO

INSERT dbo.Table1 (Column1)
VALUES (1), (NULL), (NULL), (2);
GO

-- Query 1
SELECT COUNT(*), COUNT(Column1)
FROM dbo.Table1;

-- Query 2
SELECT COUNT(*), COUNT(Column1)
FROM dbo.Table1
WHERE Column1 = NULL;

What values will be returned for each query?

2025-09-25

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

Time for a diet

One of the busiest places to be in the new year is in any gym. So many people make new year resolutions and in so many cases, it involves losing weight. So I thought I’d start the new year with a tale of a database that needed to go on a diet. The client’s primary database started at 3.8 TB. This case will be described over a short series of articles. This is part 1 and describes phase 1 of the diet.

2025-09-23

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 T-SQL transactional code that does not appear to be working as expected. The following code is being executed:

BEGIN TRAN;

UPDATE Table1 SET Column1 = 12 WHERE Column2 = 14;
UPDATE Table2 SET Column3 = 15 WHERE Column4 = 99;

COMMIT TRAN;

The second update (for Table2) is failing with a foreign key violation, but the update to Table1 is not being rolled back.

2025-09-21

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

3rd party applications and indexes

Most of my end-user clients run applications that are written by other companies ie: 3rd party applications. Very few write most of their own applications. One of the endless challenges with this is that the application vendors never want their clients to make any changes to the databases that are used by their applications. As a customer, it can be very painful to see performance problems caused by poor or inappropriate indexing choices, and yet to be blocked out from fixing those issues by supportability concerns.

2025-09-19

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: Advanced

Question:

You are reviewing a database design from one of your developers.

He normally works with PostgreSQL and in that language, he uses the text data type for all strings.

When creating the database in SQL Server, he has used the varchar(max) data type for all strings.

2025-09-17