I previously described how column data types help define what you can put in a column. But sometimes I need to be more specific.
For example, if I have an ExternalCourseRating column and it’s an integer but it’s not allowed to be any value outside the range 1 to 4, I need to do more than just say it’s an integer because that could have a wide range of potential values.
2025-03-22
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 need to add a new column to a table.
A developer insists that the column needs to be inserted into the middle of the existing table, not as a new column at the end.
2025-03-21
I showed how identity columns are a special type of constraint. They can be int or bigint. Both work just fine. What you might need to know though, is the last value inserted automatically by SQL Server.
For a long time, SQL Server only had a single option for this. It was the @@IDENTITY value.
The problem was that it could give you a value different to what you were looking for. The most common situation where this happened is if a trigger was set up. An INSERT trigger says when somebody does an insert, after it’s finished, execute this command as well. But what if that code in the trigger inserted a row somewhere else, perhaps to audit the inserts. The problem is that @@IDENTITY would return back the value from the second INSERT, not the one that you thought it was returning.
2025-03-20
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 add a computed column to an existing table.
You then select from the table.
When is the value of the computed column calculated i.e., when the value is inserted or updated, or when the value is selected?
2025-03-19
One of the most popular courses that we used to run in person was a SQL Server Administration course. Yesterday, I recently finished converting the course to an online format, and it was a big job.
I’ve had many people asking if we had this type of course. Administration is such an important skill.
We were also determined to stay with our tradition of making multi-version courses. We won’t just teach you about SQL Server 2022. Even though we’ve updated content to that version, we’ve included content for all relevant previous versions, and we show the progression across the versions.
2025-03-18
In the previous post, I talked about how you could add default values for columns.
One special type of default value is called an IDENTITY constraint. These columns are one way to achieve automatic numbering in a column. There are many pros and cons about using these but at this point, I want to make sure you know how to use them.
The main difference from other columns is that you don’t put them in your INSERT statements. In fact, unlike other types of default constraint, you cannot just put the values in there. It will raise an error.
2025-03-18
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: Intro
Question:
You need to take an additional backup copy of a database to send to another site. You are considering using the Copy Only backup option.
What exactly is different about a Copy Only backup, compared to a Full backup?
2025-03-17
Default constraints allow us to automatically provide values for columns when:
When you’re building an INSERT statement, you don’t have to give values for all columns. Columns that are declared as NULL aren’t mandatory, so you don’t have to supply those columns at all. Those columns can just be NULL.
But if you have a column that is declared as NOT NULL, so it requires a value, but you haven’t supplied it in the INSERT statement, then a default constraint can provide the value. This is configured as part of the table definition, or added as a constraint later by altering the table definition.
2025-03-16
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: Medium
Question:
You need to add additional columns to a table. You are concerned that you do not want to lock the table for long periods. You plan to avoid any operation that would rewrite every row i.e., avoid whole of data operations.
2025-03-15
Prior to SQL Server 2008, we could only insert a single row at a time. SQL Server 2008 added the ability to have multiple rows of data in the VALUES clause.
Each row is created from what are typically called row constructors. In the example above, I’m inserting 3 rows into the Cinema Groups table. The syntax allows for up to 1000 rows to be inserted at once.
Before you get to that number of rows though, you might exceed the maximum allowable length for a T-SQL statement, if you have a lot of columns, each with a lot of data. The maximum length of a statement is in theory 2GB but most people run into the batch size limit of 65536 * network packet size or about 268MB, first. Either way, it’s a lot of data in a single statement, and running into these limits is uncommon.
2025-03-14
