Fabric-Sql-Db

Upcoming processors are likely to have even more cores than now. Have you ever tried to write multiprocessor-style code? A friend of mine recently said that he learned some of this style of coding but later when he came back to it, he realised how much he thought he knew but didn’t.

For languages like T-SQL, we don’t have inherent support for multi-threading. In fact, the only trace I can see of this in T-SQL today is the ability to have multiple readers on a service broker queue.

2025-12-22

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 writing a query that involves inner joins across five tables. Does the order of the tables within the query affect the query plan?

Answer:

No. SQL Server determines the best order for you to join the tables in.

2025-12-21

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:

If you are SELECTing from a table and the ORDER BY clause in your query is in the same order as a non-clustered index, will the non-clustered index be used?

Answer:

It might or it might not.

2025-12-19

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: Development Level: Intro

Question:

A developer in your team has suggested that better formatted and laid-out SQL code will perform better?

Is this true?

Answer:

Because the optimiser reduces queries down to a format that it can work with the format of your code doesn’t make a difference. Better formatted code is more readable and maintainable though, so it’s always a good idea.

2025-12-17

SQL Server has a number of built-in database roles. The ones I see used the most are db_datareader and db_datawriter. They let you either read from all tables or read and write from all of them. Curiously, what has never been supplied is a db_procexecutor.

Developers and administrators who set up the use of these permissions think they are at least not using dbo or sa and while that’s true,

2025-12-16

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: Development Level: Medium

Question:

You have created a table named dbo.Customers. The column CustomerID has been declared as

INT NOT NULL IDENTITY(1, 1)

No contraints are defined on the table.

Can the CustomerID contain a duplicate value? If so, how?

Answer:

2025-12-15

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:

If you have two values where you want to return the first if it’s not NULL, and otherwise return the second, is there any difference at all between using the ISNULL and COALESCE functions?

2025-12-09

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:

If you pass the following string to SQL Server, will it always reliably be understood as 7th October 2025 by the date, datetime, and datetime2 data types?

'2025-10-07'

If not, why not?

Answer:

No, while that is true for date, and datetime2, the value that will be cast for the datetime data type depends upon the regional settings. For example, in British English, a string in the format ‘XXXX-XX-XX’ will be read as ‘YYYY-DD-MM’.

2025-12-06

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:

The table dbo.Customers has a clustered index CX_dbo_Customers on the CustomerID column. It also has two non-clustered indexes. One is on the CustomerName column and has an included column of PhoneNumber. The other non-clustered index is on the CityName column.

2025-12-03

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 issue the following query against the dbo.Customers table:

SELECT * FROM dbo.Customers;

The table has a clustered index on the CustomerID column.

When you have not specified an ORDER BY clause, which order will the rows be returned in?

2025-11-29