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Articles related to Microsoft SQL Server Administration

#0408 – SQL Server – Msg 1750: Could not create constraint or index


An trivial problem came to my desk recently. We were having some issues in creating a table. The script was quite simple, and yet we were facing errors as shown below.

USE tempdb;
GO
IF OBJECT_ID('dbo.ConstraintsCheck','U') IS NOT NULL
    DROP TABLE dbo.ConstraintsCheck;
GO

CREATE TABLE dbo.ConstraintsCheck 
    (RecordId INT NOT NULL IDENTITY(1,1),
     Field1   INT NOT NULL,
     Field2   INT NOT NULL
     CONSTRAINT chk_IsField2GreaterThanField1 CHECK (Field2 > Field1)
    );
GO

The script was being run via an installer, and hence all we got was the last part of the error message:

Msg 1750, Level 16, State 0, Line 7
Could not create constraint or index. See previous errors.

If you have already caught the error, great work! As for us, it took a couple of minutes and running the script via SSMS before we realized that the issue was a just a plain human error.

Here’s the full error that we got when the script was executed in SSMS:

Msg 8141, Level 16, State 0, Line 7
Column CHECK constraint for column 'Field2' references another column, table 'ConstraintsCheck'.
Msg 1750, Level 16, State 0, Line 7
Could not create constraint or index. See previous errors.

The first message that is thrown is the key – it clearly tells us that the CHECK constraint definition cannot be created because it references another column. However, this is a fairly common requirement which is what threw us off.

Finally we realized that we did not have a comma in the T-SQL script before the constraint was defined. Without the comma, SQL Server is trying to create a column constraint, when what we wanted was a table constraint. Here’s the extract from TechNet:

  • A column constraint is specified as part of a column definition and applies only to that column.
  • A table constraint is declared independently from a column definition and can apply to more than one column in a table.

So, we just added the comma to convert the column constraint to a table constraint and we were all set.

USE tempdb;
GO
IF OBJECT_ID('dbo.ConstraintsCheck','U') IS NOT NULL
    DROP TABLE dbo.ConstraintsCheck;
GO

CREATE TABLE dbo.ConstraintsCheck 
    (RecordId INT NOT NULL IDENTITY(1,1),
     Field1   INT NOT NULL,
     Field2   INT NOT NULL, --<-- A comma here makes it a legal Table Constraint
     CONSTRAINT chk_IsField2GreaterThanField1 CHECK (Field2 > Field1)
    );
GO

References:

Until we meet next time,

Be courteous. Drive responsibly.

#0407 – SQL Server – Clearing out the list of servers in SSMS


Today, I will talk about a very common question that I see in the forums. When you  work with a lot of SQL Server instances, the list of servers seen on the login screen in the SQL Server Management Studio (SSMS) becomes quite long, raising the question:

How to clear out the list of SQL Server instance names in SSMS?

SQL Server 2014 and above

Clearing out servers that no longer exist or to which you no longer need to connect to is quite simple in SQL Server 2014 and above. All you need to do is:

  1. Open SSMS
  2. In the login window,  expand the list of available SQL Server instances
  3. Use the keyboard’s down arrow or use the mouse to scroll down to the instance that needs to be deleted
  4. Once the required instance is selected in the list, just press “Delete” on the keyboard
SSMS_LoginWindow

Just select the appropriate SQL Server instance and press “Delete” to remove it from the SSMS login history

If you are still using an older version of SSMS due to various reasons, there is a manual workaround to this as shown below.

SSMS for SQL Server 2012 and below

  1. Close all open instances of SSMS on your workstation
  2. Depending upon your version of the SSMS client tools, navigate to and delete the files as shown in the table below:
  3. Launch SSMS
  4. It might take a little while to launch, as it recreates the “SqlStudio.bin”/”mru.dat
    • Once launched, you will see that the entire SSMS history is gone
SSMS Client Tools Version Path File to Delete
SQL 2012 %USERPROFILE%AppDataRoamingMicrosoftSQL Server Management Studio11.0 SqlStudio.bin
SQL 2008 %USERPROFILE%AppDataRoamingMicrosoftMicrosoft SQL Server100ToolsShell SqlStudio.bin
SQL 2005 %USERPROFILE%AppDataRoamingMicrosoftMicrosoft SQL Server90ToolsShell mru.dat

Until we meet next time,

Be courteous. Drive responsibly.

#0405 – SQL Server – Msg 5133 – Backup/Restore Errors – Directory lookup for file failed – Operating System Error 5(Access is denied.).


We got a new server recently and one of my colleagues ran into an error when restoring a database. The error was a quite generic (reformatted below for readability):

Msg 5133, Level 16, State 1, Line 1
Directory lookup for the file 
"C:\Users\SQLTwins\Documents\AdventureWorks2014\AdventureWorks2014_Data.mdf" 
failed with the operating system error 5(Access is denied.).

Msg 3156, Level 16, State 3, Line 1
File 'AdventureWorks2014_Data' cannot be restored to 
'C:\Users\SQLTwins\Documents\AdventureWorks2014\AdventureWorks2014_Data.mdf'. 
Use WITH MOVE to identify a valid location for the file.

My immediate reaction was to  review the restore script.

USE [master];
GO
RESTORE DATABASE [AdventureWorks2014]
FROM DISK = 'C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\Backup\AdventureWorks2014.bak'
WITH
MOVE 'AdventureWorks2014_Data' TO 'C:\Users\SQLTwins\Documents\AdventureWorks2014\AdventureWorks2014_Data.mdf',
MOVE 'AdventureWorks2014_Log' TO 'C:\Users\SQLTwins\Documents\AdventureWorks2014\AdventureWorks2014_Log.ldf';
GO

All looked well, I subsequently moved to the environmental aspect of troubleshooting. It was a new server and we had just created the target folders to which the database was to be restored.

We attempted to restore to the default database locations configured during SQL Server installation and the restore worked. So, one thing that became clear: the SQL Server service did not have appropriate security rights on the destination folder.

The Solution

Once we determined that it was the security rights on the destination folder, the only thing remaining was to grant the rights. Here’s how we do it.

  1. Cross-check the user set as the service user for Microsoft SQL Server database engine (use the SQL Server Configuration Manager for interacting with the SQL Server service – here’s why).
  2. Under Folder properties, ensure that this user has full security rights (or at least equivalent to the rights assigned on the default database folders specified at the time of installation)

Here’s are detailed screenshots showing the above process.

01_SQLServerConfigurationManager

Identifying the user running the SQL Server Database Engine service

02_GrantingPermissions_01

Navigating into file system folder security options to grant access to the SQL Server service

02_GrantingPermissions_02

Choosing the appropriate account running the SQL Server service

02_GrantingPermissions_03

Applying appropriate rights to folder

By the way: If you encounter similar issues in accessing your backup files, the root cause and solution are the same. Check the permissions on the folders housing your backups and you should  see that the database engine does not have the necessary security rights.

Further Reading

Maintaining permissions on data folders and appropriate registry entries is something that is handled by the SQL Server Configuration Manager when you change the service account under which  the database engine is running. If you use services.msc (the old way), this is not done and your SQL Server may stop working.

  • Changing SQL Server Service Account or Password – Avoid restarting SQL Server [Blog Link]
  • Blog Post #0344 – SQL Server – Missing Configuration Manager on Windows 8 [Blog Link]

Until we meet next time,

Be courteous. Drive responsibly.

#0404 – SQL Server – Interview Question – What is logical data integrity?


Recently, I encountered an interesting question in one of the forums:

What is logical data integrity?

The person who posted the question was reading about SQL Server and databases in general, when this term was encountered. Because the answer to this question can help clarify one’s understanding of data design  concepts, I thought it would also make a very interesting interview question as well.

Today, I try to describe that data integrity is.

What is data integrity?

Data is a critical part of any business. But, data by itself holds no value. For data to be information of business value, it needs to be valid with respect to the business domain.

A piece of data may be perfectly acceptable from the physical design perspective, but may be still be invalid for the domain.

Let’s take an example – a rate of 2000 is perfectly acceptable for an integer. That is physical data integrity – the value is valid with respect to the physical design of the database. But, if  we are talking  about an application that captures and analyzes patient/medicinal data, the rate of 2000 is totally invalid and indicates some sort of logical bug/corruption.

Other examples would be a meeting end date that’s less than the meeting start date or a business/person without a name.

A data point may not be acceptable within the business rules defined for a domain. Similarly, what’s valid as a data point for one domain may be invalid for another domain. Ensuring that your database only accepts valid values with respect to your domain is what I call logical data integrity”.

Types of Data Integrity

Logical data integrity can be enforced in two ways:

Declarative Data Integrity

If data  integrity is enforced via the data model (implemented via the Data-Definition-Language, i.e. DDL), it is declarative data  integrity. One would enforce declarative integrity via the elements of the table definition:

  • Appropriate Data-Types
    • In our example for the medical domain, it would limit the possibility of corruption if a TINYINT is used to store the heart rate instead of an INT
  • Primary Keys
    • Avoid the insertion of duplicate data!
  • Foreign Keys
    • Ensures that all references are known (it is a valid primary key in another table)
  • Default, Check, Unique and Not-NULL constraints
    • Unique and Not-NULL constraints help maintain uniqueness and avoid insertion of unknown (NULL) data
    • Usage of default constraints ensure that by default unknown (NULL) values are replaced by valid default values
    • Check constraints help ensure that data meets the valid range defined by the business (e.g. a check constraint would help ensure that the meeting end date is greater than or equal to the start date)

Procedural Data Integrity

Legacy applications (I have worked on a few that match this description) which were originally developed in the days of flat-file databases, often used procedural code to enforce data integrity.

When these were migrated to Microsoft SQL Server, the integrity was enforced via stored procedures and triggers to avoid re-engineering the database structure and changing the application code to match the new structure.

Data integrity enforced via code, i.e. via stored procedures, triggers and/or functions is called procedural data integrity.

My take: Procedural code can be disabled, fail or have bugs. This may cause the application code to generate bad/invalid data rather than prevent it.

I believe procedural data integrity is acceptable as long  as it is used as a “fail-safe” mechanism. The primary mechanism to ensure logical data integrity should be declarative in nature, in my humble opinion.

The above is my take on logical data integrity. I welcome your thoughts on the subject in the space below.

Until we meet next time,

Be courteous. Drive responsibly.

#0402–SQL Server 2016 – KB3207512 fails–Msg 17054 – Unable to shutdown the instance; Operating System Error 21 (The device is not ready)


I recently updated my personal sandbox to use SQL Server 2016. While the installation succeeded, one of the first few problems that I ran into were:

  • The SQL Server 2016 instance failed to shutdown
  • Error 17054 was logged every time a shutdown is attempted with the error: “The current event was not reported to the Windows Events log. Operating system error = (null). You may need to clear the Windows Events log if it is full.
  • Installation of KB3207512 (update for SQL Server 2016 SP1 Reporting Services) and latest CUs kept failing
  • User databases would not be accessible with an error: “The operating system returned error 21(The device is not ready.)

While I was trying to figure out what was wrong, I ran into the same problem with a few other instances.

The Solutions

After a lot of rounds of trial and error, the following changes finally did the trick. The items below collectively make up the solution and all items need to be performed in order to get the SQL server instance up-to speed again.

  • Launch the SQL Server Configuration Manager
  • Under “SQL Server Network Configuration” ensure that the TCP/IP protocol is enabled
  • Under “SQL Server Services”, ensure that the following services are started:
    • SQL Server PolyBase Engine
    • SQL Server PolyBase Data Movement

Once the steps provided above are done, all the problems listed above should cease to exist.

Until we meet next time,

Be courteous. Drive responsibly.