Azure-Sql-Db

One of SQL Server’s greatest strengths is its ability to execute queries in parallel. When parallelism is available, the engine can divide work across multiple CPU cores and dramatically reduce query duration for large or complex workloads.

Yet in real systems, it’s surprisingly common to find queries that could run in parallel but don’t. The reason is often not hardware, configuration, or cost threshold settings — but query anti-patterns that quietly force the optimizer into a serial plan.

2026-01-26

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

Today’s tale relates to a SQL Server system that had wonderful hardware, yet was unbelievably slow. Let’s discuss what happened.

Some background information

I had a call from the Microsoft office in Brisbane, Queensland, asking if I had time to look at a problem at a customer site. Both they, and the customer, had thrown considerable resources at trying to resolve a performance problem, but frustratingly, it persisted.

2026-01-24

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:

A database backup was started at 12:00 PM. It completed at 2:00 PM.

When the backup is restored, at what time point will the restored data be?

• 12:00 PM
• 2:00 PM
• Somewhere between 12:00 PM and 2:00 PM

Answer:

2026-01-20

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 have tables that have both constraints and triggers. You need to explain the order of execution for these. Which execution order (from first to last), are used for:

• Check constraints
• After triggers
• Instead of triggers

Answer:

2026-01-18

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:

If a database is configured for simple recovery model, what could stop the truncation of the transaction log being effective, and for the transaction log to keep growing in size?

Answer:

Here are the most frequent reasons:

2026-01-16

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: Intro

Question:

You are restoring a database backup. The restore finished reading pages 10 minutes ago, but the database still shows that it is restoring.

Can you speed up the restoring phase by restarting the server? If so, should you do that? If not, why not?

2026-01-14

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: Intro

Question:

You have a database configured for simple recovery model. You notice that the transaction log is still increasing in size.

What could cause this?

Answer:

Even in the Simple recovery model, it is quite normal to see the transaction log file grow. That does not necessarily mean it’s stuck or misconfigured.

2026-01-12

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 reviewing the memory usage of a Windows Server running SQL Server. It appears to have almost run out of memory.

You add additional memory, and monitor the usage of the memory by SQL Server. It appears to always be constantly increasing, until the server is almost out of memory again.

2026-01-10

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: Intro

Question:

You are reviewing the design of a database and note that in the dbo.Customers table, there is a column called CustomerTimestamp that has the timestamp data type.

Can you extract the date from the CustomerTimestamp column by using the CONVERT function?

2026-01-08

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 tracing queries using Extended Events. Two queries have exactly the same execution plan, and the same plan costs. In the trace, one query showed a duration of 2 minutes. The other query showed a duration of over an hour.

2026-01-07