Grouping dates without blocking operators

It’s not entirely uncommon to want to group by a computed expression in an aggregation query. The trouble is, whenever you group by a computed expression, SQL Server considers the ordering of the data to be lost, and this will turn your buttery-smooth Stream Aggregate operation into a Hash Match (aggregate) or create a corrective Sort operation, both of which are blocking.

Is there anything we can do about this? Yes, sometimes, like when those computed expressions are YEAR() and MONTH(), there is. But you should probably get your nerd on for this one.

Continue reading

Encrypting SQL Server connections with Let’s Encrypt certificates

Encrypting your SQL Server’s TDS connections should be high on your list of things to do if you’re concerned with the privacy of your data. This often boils down to one big problem: can you get a valid certificate without paying a ton of money, and will it work with SQL Server?

So follow me down the rabbit hole, as we work out the steps to using Let’s Encrypt to create (and auto-renew!) a certificate for SQL Server. This is going to get technical.

Continue reading

Key Lookup without an output column?

Performance tuning the other day, I was stumped by a query plan I was looking at. Even though I had constructed a covering index, I was still getting a Key Lookup operator in my query plan. What I usually do when that happens is to check the operator’s properties to see what its output columns are, so I can include those columns in my covering index.

Here’s the interesting thing: there weren’t any output columns. What happened?

Continue reading

Catching circular references in parent-child structures

A popular form of organizing dimensions is in parent-child structures, also known as “unbalanced” or “ragged” dimensions, because any branch can have an arbitrary number of child levels. There are many advantages to this type of representation, but their recursive nature also brings some challenges. In this post, we’re going to look at circular references, and how you can trap them before they run out of control.

Continue reading