If you’re a consultant connecting to remote client servers, or if you have a heterogenous network environment with different Active Directory forests without established trust relationships, you’ll have a few extra challenges connecting to SQL Server using Windows authentication, and SQL Server authentication may not be available.
Author: daniel
Copying data with foreign keys and/or identity columns
In a sense, you could call me lazy. If there’s a script that will perform a task for me, I’d rather use that script than reinvent another wheel. Then again, if needs be, I’d rather spend a day writing such a script, rather than spending ten minutes just getting the job done.
Somehow, that makes me a happier developer.
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:
Calculating the number of weekdays between two dates
I wish the DATEDIFF() function would count the number of working days (mondays through fridays) between two dates for me, but until that happens, I’ve had to roll my own scalar function. I tried to think of a smart way involving perhaps a modulus calculation, but I quickly succumbed to a more down-to-earth approach.
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.
A faster Fibonacci series in T-SQL
Fibonacci’s numbers are a sequence of numbers calculated using a recursion pattern that typically lends itself more to procedural programming. This makes it trickier to implement in a well-performing solution in T-SQL, as T-SQL is set-based.
Windowed DISTINCT aggregates
You may have discovered that the use of DISTINCT is not supported in windowed functions. A query that uses a distinct aggregate in a windowed function,
SELECT COUNT(DISTINCT something) OVER (PARTITION BY other) FROM somewhere;
will generate the following error message:
Msg 10759, Level 15, State 1, Line 1 Use of DISTINCT is not allowed with the OVER clause.
There are, however, a few relatively simple workarounds that are suprisingly efficient.
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.
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.