Voice of the DBA

Author: way0utwest

Changing NULL to NOT NULL – Dealing with Data

I wrote recently on how to alter a column in SQL Server from NULL to NOT NULL in a simple way. However I didn’t cover some of the cases where you have data in the column, or other restrictions that you might need to deal with. In this post, I want to look at a few options if you have data in the table.

Let’s take my SimpleTable and add data:

INSERT Simpletable VALUES (1, ‘A‘, 1) , (2, ‘B‘, 0) , (3, ‘C‘, NULL) , (4, ‘D‘, NULL) ;

Now I have 4 rows. If I run this:

ALTER TABLE dbo.SimpleTable ALTER COLUMN Status TINYINT NOT NULL;

I get this error:

Msg 515, Level 16, State 2, Line 2

Cannot insert the value NULL into column ‘Status’, table ‘Sandbox.dbo.SimpleTable’; column does not allow nulls. UPDATE fails.

The statement has been terminated.

Essentially, SQL Server can’t mark this column as NOT NULL because there are NULLs in there. What can I do here?

UPDATE the Table

The only thing I can do is to change the data. I can run a query that removes all the NULLs in the column by setting them to some value. That’s what I’ll do here. I can choose a value here and run an UPDATE statement. Something like this:

UPDATE dbo.SimpleTable SET Status = 0 WHERE status IS NULL;

Once I do that, I can easily run my ALTER and it succeeds.

May 25, 2015
Unit Testing in Philadelphia
I’m helping teach a pre-conference session on Friday, June 5, 2015 at the Microsoft office in Philadelphia. This is an all day, paid for event, that looks at how you can use a framework to write unit tests for your T-SQL code. We’re the day before SQL Saturday #390 in Philadelphia

I really believe in testing, and am trying to advocate for it in many places. I’ve delivered a testing session that has been well received at quite a few events and this is the first time I’m trying a full day training class.

I am working with Sebastian Meine, the founder of tSQLt, to present the class. We’ve got a busy outline, looking at a variety of ways that you can write tests and use them to find problems in code. Here’s what we’re covering.
- Introduction to Unit Testing
- What is tSQLt?
- Your First Test
- Executing Tests correctly
- Effective use of Assertions
- Separation of Concerns
- Testing Exceptions
- Test Case Heuristics
- Dealing with Test Data
- Other Types of Testing
- How Unit Testing fits into your Development Process
At the end of the class, you should have some good ideas on how to build and structure tests in your own environment and be ready to start testing on Monday.

I hope to see you there, and register today if you want to learn more about unit testing in SQL Server.
May 22, 2015
Native Audits

As our databases contain more and more information, it is becoming increasingly more common to implement some sort of auditing feature to ensure that our data is not being inappropriately accessed or altered. It’s not only the management of our organizations, but also regulatory rules are becoming more numerous, and some may think onerous, which increases the burden on the DBA.

There are numerous products available to help here, but SQL Server has included it’s own internal features since SQL Server 2008. However, it seems that I encounter many people that are unaware of the SQL Server Audit feature, and indeen, may not be aware of the Extended Events system on which it’s based. This week I wanted to ask if you are using this feature.

Are you using SQL Server’s native Server Audit and Database Audit features?

If you can share and reasons or details on how you are using the audits, or how easy it is to administer them, it would be interesting. I think we do need to increase the level of auditing on our systems at least to ensure that we are not experiencing any inappropriate data access. At a minimum, we should be monitoring for privileged level access or account changes.

Steve Jones

The Voice of the DBA Podcast

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May 22, 2015
DB_Owner Querying for Database Options

Another post for me that is simple and hopefully serves as an example for people trying to get blogging as #SQLNewBloggers.

What can a user with the db_owner database role do? I assumed anything inside of the database (create/alter objects, assign permissions, back up the database, etc). However someone asked recently about whether someone could read database properties. I’d assume they can, but I needed to check.

I decided to start by creating a new login. I have lots on my test instance, but I went with just building a new one. I used the GUI to add [DBOwnerTest] because it’s quicker. I assigned a password, set a default database, and mapped this user to db_owner in a database.

I then opened a query window and changed the connection:

Now I could easily run a query for properties and see the results:

Note the connection at the bottom of the image above.

Here’s where it’s a little interesting. I disconnected Object Explorer and connected back as DBOwnerTest. I see this:

Looks normal. According to the BOL documentation for permissions, db_owner gets View Any Database as well as control over their own database. I can see the properties of the Sandbox database (where I’m db_owner).

But I can’t see properties of other databases.

I also see my login, but not the couple dozen others I have, other than sa. That’s curious, and perhaps not good. However this isn’t the place to delve into that.

I have the ability to query through databasepropertyex(), which I’ve documented in another post.

Certainly db_owner conveys lots of rights to the user, and certainly the ability to see some of the outside of the database container, such as the options and properties, as well as other databases.

Writing

This was based on a question I saw posted at SQLServerCentral. It took me about 5 minutes to set up a test login and query for information. I had to perform a few searches and try some queries. I spent a few minutes researching databasepropertyex(), which became another post.

All told, this was about a 15 minute post.

You can do this. Join the #SQLNewBlogger group and start documenting your career. You can see all my posts that fall into this area by looking through the SQLNewBlogger tag here.

References

Permissions of Fixed Database Roles – https://technet.microsoft.com/en-us/library/ms189612%28v=sql.90%29.aspx

May 21, 2015