An interesting discussion/question in the SQL Community Slack today arose around how to implement blue/green deploys.
If you’re not familiar – blue/green refers to a deployment strategy with at least two hosts of your services, where you host in the green, deploy to the blue, and slowly drain the green to the blue until it becomes the green.
This has consequences in terms of keeping the lights on for both services, potentially rolling back the traffic to the green node (if the blue deployment fails some tests) and identifying things like dead code/data paths.
I was pondering how to answer the question in anything but the most generic way when this youtube video by Kevin Feasel was posted and it’s such a great resource I’m reposting it.
An interesting question asked by @danthesqlman in #sqlhelp (sqlcommunity.slack.com)
Having issues with Unicode in my XML, tried using a try_convert(varchar,fieldname) but not returning NULL. Set it to have a test on my box, and weird results. declare @n nvarchar(10) = N’ניקודות’ select try_convert(varchar(10),@n) This doesn’t return NULL, but ????????? I’m curious what would I be doing wrong, or how can i locate unicode within XML easily
And then when people suggested individual character shredding –
XML documents in a table over 200k rows, 2mb xml each, could take hours to parse 1 character at a time
There were a few suggestions, (my initial crap one was just dumping it to C#), but after a few jokes back and forth about how SQL Server was just returning normal question marks for TRY_CONVERT and how silly that was the idea came up… why not just:
Replace all question marks with something unique? (I suggested a GUID)
Run the conversion and then do a reverse replace, updating the data in place.
For a simple code example…
DECLARE @magic_value UNIQUEIDENTIFIER = NEWID() SELECT TRY_CONVERT ( VARCHAR(100), REPLACE(tar.name,'?',@magic_value) ) FROM target_table AS tar
Any new question marks that exist in the output would be characters that failed the conversion process.
The test ran in ten minutes instead of a few hours… great!
To be clear – I think you should be updating your PowerShell regularly, however the HUGE WHITE BLOCK ACROSS MY ENTIRE SCREEN EVERY TIME I LAUNCH VISUAL STUDIO CODE ISN’T GREAT.
Hated that caps? Yeah, that’s basically my eyes every time I see this nag window inverting the colors across my ennntiiirrreee screen.
I checked the PS repo and some one liners posted didnt work (and used SetEnvironmentVariableTarget which was not a method I had?), so I wanted to make this easy in case you are getting frustrated with the PowerShell update version check message and you want it to go away and didnt want to crack open the environment variables.
I have been busy working on some other non-SQL related side projects recently, and I wanted to note some of the pieces of code I have been appreciating recently.
https://github.com/PaesslerAG/django-currentuser is a simple plugin that allows you to reference your current user context in your models various functions. This greatly simplified some user management functions within my codebase, as I could express it all in the model.
https://www.django-rest-framework.org/ is a powerful framework on top of Django that allows you to build a straightforward rest framework. Django doesn’t have object based permissions and I have been building out the next version of my codebase with it, its definitely a lot more pluggable than anything I designed.
So a friend of mine had a query puzzle – he needed to print some W2 forms but the forms themselves only allows up to 4 groups of a value to be placed in a box or else they’d need to issue two forms.
The pickle is that the source data is freeform csv text, so what can we do on the database side?
I reached for my handy CROSS APPLY, a numbers table, windowing functions and a little modulo arithmetic – its not so bad to return a subgroup within a group in SQL as long as you are willing to lay out additional columns to count your grouping.
Today I was diving into some extremely wide tables, I wanted to take a quick look at things like “How many unique values does this table have in every column?”.
This can be super useful if you have a spreadsheet of results or a schema without effective normalization and you want to determine which rows are the “most unique” – or have high cardinality.
The Github gist is embedded at the bottom of the page, but I will run you through the code in case you want an explanation of how it works
The procedure takes a schema and a table/view name and combines them – I could ask the user to do this for me, but there’s parts where its useful to break them up and I dont want to mess with split logic :p
The procedure is defined as a temporary stored procedure as I didnt want to leave a trace when I disconnect.
I then define the dynamic UNPIVOT statement, which we will feed our dynamic column listing from.
Gather our columns (twice) – once for the COUNT(DISTINCT), and once for the use in the columns we want to UNPIVOT.
Here’s an example of running it against a tsqlt testresult table:
As we can see, the tsqlt testresult table has one class, two messages and results, and unique everything else (so that’s where I will focus.)
I also utilize a @magic_value variable in the code (not shown) which I use to deal with the fact that a NULL value in an UNPIVOT statement wont count as an occurrence. I want to disambiguate from NULL and any particular value that might occur, so using something like -1 or some string NULL would be inappropriate.