With good naming and datatyping conventions, an automated script can help you with the process of creating foreign key constraints across your database, or actually, suggest table relations where you’ve forgotten to implement them.
SQL Server concepts
Practical uses of binary types
The binary datatype of SQL Server is one of those features most developers don’t really use that often, but it turns out there’s more to binary values than just storing large, non-relational blobs.
A visual representation of SQL Server Agent jobs
If all you have is a hammer, everything will eventually start looking like a nail. This is generally known as Maslow’s hammer and refers to the fact that you use the tools you know to solve any problem, regardless if that’s what the problem actually needs. With that said, I frequently need a way to visualize the load distribution of scheduled jobs over a day or week, but I could never be bothered to set up a web server, learn a procedural programming language or build custom visualizations in PowerBI.
So here’s how to do that without leaving Management Studio.
Availability Groups: How to sync logins between replicas
AlwaysOn Availability Groups are a reasonably simple way to set up disaster recovery (DR) for your SQL Server environment, and with fairly little effort, you can get a bit of high availability (HA) from it as well. But there are a few gotchas, the most obvious of them being that Availability Groups only synchronize specific user-databases, not the entire server setup.
Things that are not included in AGs include logins, SQL Server Agent jobs, SSIS packages stored in SQL Server, linked servers and server settings. You could sync these manually (as is often the case), but wouldn’t you just love to have an automated process do all this for you?
This is the first post in a series on synchronizing stuff between Availability Groups, and in this installment, we’ll look at logins. For the sake of simplicity, I’ll assume that you have a primary replica with a single AG and any number of secondary replicas. The logic holds true if you have multiple AGs, it just gets trickier.
Video: three SQL Server join operators in three minutes
In an attempt to try a different approach, here’s a three-minute video explanation of how the different physical join operators in SQL Server work and why you would choose one over the other.
More reading
I’ve written a few blog posts on join operators befores, so if this video wet your appetite, here’s some recommended reading:
I’d love to hear what you think of the short video format! Please leave feedback in the comments below or on Twitter.
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?
Selectively disable “Include actual execution plan”
The “include actual execution plan” feature in SQL Server Management Studio is an invaluable tool for performance tuning. It returns the actual execution plan used for each statement, including actual row counts, tempdb spills and a lot of other information you need to do performance tuning.
But sometimes you want to run a series of statements or procedures where you only want the execution plan for some of the statements. Here’s how:
Detaching a database also alters file permissions
Moving a database or some of its files from one drive to another or from one instance of SQL Server to another is as simple as detaching it and re-attaching it again. This is actually pretty smart, compared to backup–restore, because you only perform one I/O operation (moving the file), as opposed to two (backing up, restoring).
But when you try to attach the database, you might get something like
Msg 5120, Level 16, State 101, Line 3 Unable to open the physical file "E:\Microsoft SQL Server\SQL2014\MSSQL\Data\Playlist.mdf". Operating system error 5: "5(Access is denied.)".
The reason, as I found out the hard way, is that SQL Server can actually modify the file permissions of the .mdf and .ldf files when it detaches a database.
Last row per group
A very common challenge in T-SQL development is filtering a result so it only shows the last row in each group (partition, in this context). Typically, you’ll see these types of queries for SCD 2 dimension tables, where you only want the most recent version for each dimension member. With the introduction of windowed functions in SQL Server, there are a number of ways to do this, and you’ll see that performance can vary considerably.
Different query plans for “OR” type queries
The SQL Server query optimizer can find interesting ways to tackle seemingly simple operations that can be hard to optimize. Consider the following query on a table with two indexes, one on (a), the other on (b):
SELECT a, b FROM #data WHERE a<=10 OR b<=10000;
The basic problem is that we would really want to use both indexes in a single query.
In this post, we’re going to take a look at a few examples of how this type of query would be optimized, as well as how statistics can affect the query plan, and finally, we’ll take a look at a slightly rare plan operator called “Merge Join (Concatenation)”.
