Sql-Server

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 have applications that make extensive use of NOLOCK hints. You have heard that this can cause issues.

Which of the following issues could occur as a result of using NOLOCK hints?

Duplicate rows
Phantom rows
Missing rows

Answer:

2025-08-16

SQLCMD mode changes how queries are executed in SSMS. When using this mode, you can work with options that aren’t normally part of SQL Server T-SQL scripts.

Some installation scripts also require SQLCMD mode and will fail if it’s not enabled.

Let’s look at an example executing a query against 2 servers within the same script.

First, we open a new query window, then on the Query menu, we choose SQLCMD Mode.

2025-08-15

If you look at the code in the image above, I have one immediate reaction.

What are those numbers that are sprinkled throughout the code?

I see this all the time in T-SQL code. Yet in any programming language, it’s a really poor idea to do this. It leads to very fragile code that’s so hard to maintain longer-term.

So why do people do it?

So, you might wonder why people do this in T-SQL. Couldn’t they just do this at the start of the code?

2025-08-14

In an earlier entry, I mentioned how useful the F1 key is. On its own, it provides syntax help, but when you highlight an object and hit Alt-F1, you get to see metadata about the object.

Under the covers, this just runs the sp_help system stored procedure. Alt-F1 has been mapped to that.

You can see where this is configured, change it if required, and/or configure other procedures as well.

2025-08-13

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:

When you rebuild indexes, are statistics on the table automatically rebuilt?

If not, why?

Answer:

Rebuilding indexes updates the statistics for the index, but column statistics are not updated unless they are tied to the index.

2025-08-12

While SQL Server is quite fast at executing queries, when you are connecting from a client application like SSMS, you might wonder how much time SQL Server spent executing the query, as opposed to how long the communication with the server took.

This type of information is available in the Client Statistics.

Let’s see an example. If I connect to a server in an Azure data center, I’ll have higher latency than for one in my own site. That will affect the wait time for a server response. I’ll connect to a server that I have aliased as SDUAzure. The server is in the Australia South East data center.

2025-08-11

Years ago, I was a trainer for the Microsoft SQL Server Master’s program at their headquarters in Redmond. In one of the labs, I asked the students to set up database mirroring on a TDE-encrypted database. It was fascinating to watch them try to set it up.

It’s important to realize that the students in the room were all Premier Field Engineers and senior consultants from Microsoft and from some large partner companies. The students were all very experienced with the product. Yet it often took many of them quite a while to work out how to set it up.

2025-08-10

In T-SQL, a script is a set of one or more batches.

For example, if we have the following script and click Execute, it looks like all the commands were sent to the server and executed all at once:

But that isn’t what happened.

What did happen is that SSMS found the word GO and broke the script into a series of batches. In this case, there were three batches. First, it sent the commands shown here as Batch 1 to the server, waited for them to execute, then sent Batch 2, waited for it to execute, then sent Batch 3, and waited for it to execute.

2025-08-09

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: Administration Level: Medium

Question:

You are monitoring a SQL Server and you notice that tempdb is being heavily accessed. You know that your applications make very little use of temporary tables.

Can you give examples of other things that might be using tempdb.

2025-08-08

In an earlier post, I mentioned that you can create a registered list of servers, either in Local Server Groups or stored in a Central Management Server.

What I didn’t really talk about though, is what you can do with these groups of servers, rather than just executing queries on an individual server.

I’ve created three local server groups, for my development, UAT, and production servers.