T-SQL Tuesday #86: SQL Server Bugs & Enhancement Requests

The Good, the Bad, and the Bug-ly.

Advertisements

The Good, the Bad, and the Bug-ly.

This month’s T-SQL Tuesday is brought to us by Brent Ozar ( work | personal | tweets ) and has to do with SQL Server Bugs and Enhancement requests on Microsoft Connect.

Now the reason that this is the topic of this month’s T-SQL Tuesday is nicely spelled out by the host himself:

Now, more than ever, Microsoft has started to respond to Connect requests and get ’em fixed not just in upcoming versions of SQL Server, but even in cumulative updates for existing versions.

If you’ve kept an ear to the ground and an eye out on the social media, (seriously get on Twitter if you haven’t already; with #sqlhelp and #sqlfamily, you’ll never be alone, stuck, and/or bored again), you’d realise that this is true. Microsoft has engaged more than ever with it’s audiences, from hiring a PowerShell developer to actively engaging in various Trello Channels. So much so that a twitterbot was created to keep track of Connect items closed as fixed (Closed As Fixed) by MVP Chrissy LeMaire ( blog | tweets ).

Shameless Plug:

Now, I happen to have a Connect item and I’m going to link to it here. I can do this as this blog shares a commonality with Lesley Gore’s birthday party song. (It’s mine and I can cry if I want to)

The Good…

First of all, lets see what we’re running on here…

SELECT @@VERSION

 

 

version
I really should be doing these against SQL Server 2016… 😦

First contender: Inserting to an indexed view can fail

What would happen if I told you that, with regards to a view, sometimes inserting into the table could fail? Well that’s what this Connect item from Dave_Ballantyne found, along with the reason.

CREATE TABLE myTable
(
    Id integer not null,
    InView char(1) not null,
    SomeData varchar(255) not null
)
GO

CREATE VIEW vwIxView
WITH SCHEMABINDING
AS
SELECT 
    ID, 
    Somedata, 
    LEFT(SomeData, CHARINDEX('x', SomeData) - 1) AS leftfromx
FROM 
    dbo.myTable
WHERE 
    InView ='Y'
GO

CREATE UNIQUE CLUSTERED INDEX pkvwIxView ON vwIxView(Id)
GO

 

 

Now that we have the groundwork laid out, it’s time for our insert attempt:

DECLARE @id integer,
@inview char(1),
@Somedata char(50)

SELECT @id = 1,
@inview = 'N',
@Somedata = 'a'

INSERT INTO myTable(Id, InView, SomeData)
SELECT @id, @inview, @Somedata

 

daveballantyneerror
Do you see a LEFT() or SUBSTRING() ANYWHERE there???

He’s even gone so far as to give an explanation as to why this happens!

This is due to the compute scalar being executed prior to the filter.

Taking a look at the estimated execution plan, we can see that he’s right!

daveballantyneerrorplan
Let’s do it first, then see if we should have!

Imagine trying to troubleshoot what was causing the inserts to fail? Horrible! I can imagine tearing my hair out at that one!

I have this done as “The Good” just for the fact that, not content to just report the bug, Dave_Ballantyne even went so far as to find the possible cause. Now it’s just up to Microsoft to get to the fixing…

…The Bad…

Next up, we have moody31415 with “Can’t create Materialized View that references same table twice

Groundwork:

CREATE TABLE test (A int)
GO
CREATE VIEW vtest WITH SCHEMABINDING
AS
SELECT t1.A, t2.A as A2
FROM dbo.test T1
JOIN dbo.test T2 ON T1.A=T2.A
GO

The problem occurs when we try to add a unique clustered index on this bad boy:

CREATE UNIQUE CLUSTERED INDEX UCL_Test
on dbo.vTest (A, A2)

 

maddog_selfjoinviewserror
Ever get those times where you just can’t stand yourself?

Now, I originally put this down as “The Bad” because I thought that the issue could be down to trying essentially index the same column twice but that’s not the case…

CREATE TABLE dbo.B (col1 tinyint, col2 tinyint)
GO
CREATE VIEW dbo.SecondOne
WITH SCHEMABINDING
AS
SELECT t1.col1, t2.col2
FROM dbo.B AS t1
JOIN dbo.B AS t2 ON t1.col1 = t2.col1
GO
CREATE UNIQUE CLUSTERED INDEX UCL_test
ON dbo.SecondOne (col1, col2)

 

maddog_selfjoinviewserror_02
…I mean After-A-Massive-Meal-Cant-Stand-Yourself

In the end, the reason that I have this in “The Bad” section is that I went to the documentation and read this part…

The SELECT statement in the view definition must not contain the following Transact-SQL elements: […] self-joins […]

Now it’s unknown whether this was there when this Connect item was created, but it’s there now (and I didn’t have enough time to re-plan this blog post)

…and The Bug-ly.

In my quest through the magical lands of Connect I stumbled across this little beauty of a bug by Anatoly V. Popov that I had to mention as “The Bug-ly”.

Altering indexed view silently removes all indexes

Yes, I know it’s the same as my one but dammit if I don’t think it’s a bug! That’s why it’s getting my “The Bug-ly” title.
This leaves me with a bit of a conundrum though…Do I close mine and comment on this one to get re-opened? Or do I try and continue to push on my one?

To be honest I don’t know which option to choose but, for anyone new to SQL Server, filing a Connect Item is an exciting but nerve-wracking time.
Exciting because you’ve worked with SQL Server enough to think you know how something should be done.
However, it’s nerve-wracking because you haven’t worked with SQL Server for long enough to know if you are just whining or have an actual item to be taken seriously.

Finding this Connect item was a small little shot of validation for me. Just a little something to say “Hey, I thought this too and I’m with you”.

Summary

It’s a great thing that Microsoft have started to respond to the Connect Items again and going through them you realise how different people are using SQL Server in ways that you didn’t even think to imagine.

So check out a few, leave your comment and up-vote/down-vote as you see fit.

Just…just don’t be this guy please

dt_ofdbas

 

 

Author: Shane O'Neill

DBA, T-SQL and PowerShell admirer, Food, Coffee, Whiskey (not necessarily in that order)...

One thought on “T-SQL Tuesday #86: SQL Server Bugs & Enhancement Requests”

What's your opinion?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s