The Bit Bucket

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: Query Performance Level: Medium

Question:

In SQL Server a column that is defined with a bit data type can only have the values 0, or 1, or it can be NULL if the column allows it.

Given such a small number of possible values, are bit columns ever useful in indexes? Can you give an example of when they might or might not be useful?

2021-03-26

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:

When you are writing a CREATE TABLE statement to define a new table, after each column, you can write NULL or NOT NULL, but doing that is optional.

Why is it a good practice to include it, and what happens if you leave it out? Are the columns defined as NULL or as NOT NULL? Are there any exceptions to this?

2021-03-25

I have a lot of people who recommend books to me. I order many of them. If the book has impressed one of my friends, I’m keen to see what they liked about it. That’s how I came to read Living Forward: A Proven Plan to Stop Drifting and Get the Life you Want by Seth Godin.

The title is making a pretty big claim, but the content? It’s ok.

2021-03-24

Dynamic Data Masking was added to SQL Server back in 2016. I’ve almost never used it since. Why? There were two reasons:

#1: The first reason was that it didn’t work in conjunction with other security features. In particular, you couldn’t use dynamic data masking in conjunction with Always Encrypted. From the start, I’ve been telling the product group that this is a misstep. There’s very little data that I’d want to hide from my own staff, that I’m happy still being visible to a hosting provider.

2021-03-23

In my last T-SQL 101 post, I mentioned ROW_NUMBER. It let you put a row number or position beside each row that was returned. Sometimes though, you want a rank instead. A rank is similar but it’s like a position in a race.

In the example above, I’ve used RANK to produce an ordering, based on an alphabetical listing of city names. Notice there’s Abercorn Abercorn Abercorn and then Aberdeen. So, like in a race, if three people came first they all get the value 1. The next person is fourth. Three people came forth, so then the next one is 7th, and so on.

2021-03-22

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: Security Level: Medium

Question:

I have an application that connects to the database as a user called ReaderApp. The only role that ReaderApp has been added to is db_datareader. The application was previously only using SELECT statements to read data that was required.

2021-03-19

Many clients hire me to carry out job interviews on their behalf. If they’re hiring someone for a data-related role, they want to make sure they’re hiring the right person. That usually means two things:

• The person will fit well within the culture of the organization
• The person is technically competent.

I can’t help with the first one. If I’ve worked with the client for a long time, I might have a pretty good idea but ultimately, that’s something the client needs to decide.

2021-03-18

A few weeks back, I finished reading The Lean Startup: How Constant Innovation Creates Radically Successful Businesses by Eric Ries.

There have been a lot of books on Lean methodology over the years, so I didn’t know what to expect with this one. But it was published back in 2001 (i.e. the turn of the century) and that’s when the Lean methodology was still fairly new in entrepreneur circles.

I’ve seen others comment that this was the “single most informative book on the iterative entrepreneural process”.

2021-03-17

I’ve been amazed as the pandemic has continued, how many companies that claim to understand remote work, still really don’t get it. I’ve decided that a good test of that, is whether job advertisements still show a city or location for the work.

Now, not everyone can work remotely, and not everyone has anywhere suitable to work from remotely, but the majority of knowledge workers can do just that. That’s who I’m talking about here.

2021-03-16

In SQL Server 2000 and earlier versions, I often heard people ask “How do I output a row number beside each row that’s output in my query?”

I remember some people arguing that it wasn’t a valid request, as it didn’t feel “set-based” but it was an appropriate request, and it could be dealt with in a set-based manner. Sometimes it’s very, very useful to be able to do that.

2021-03-15