Category: Errors and Exceptions

Errors and Exceptions, SQL

Error Message: “The database could not be exclusively locked to perform the operation.” in SQL Server

Recently we encountered an error message as below while doing a rename database. So, let us look at the steps that we can use to overcome the issue with this post.

The database could not be exclusively locked to perform the operation.

We were trying to rename a database in one of our lower environment as below and ended up with the error message.

ALTER DATABASE dbname MODIFY NAME = dbname_new

Steps to resolve

  1. Take the database to single_user mode
  2. Rename the database
  3. Take the renamed database to multi_user mode

Script

ALTER DATABASE dbname SET SINGLE_USER WITH ROLLBACK IMMEDIATE
GO
ALTER DATABASE dbname MODIFY NAME = dbname_new
GO
ALTER DATABASE dbname_new SET MULTI_USER WITH ROLLBACK IMMEDIATE

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Errors and Exceptions, SQL

Warning Message in SQL Server: “Database name ‘tempdb’ ignored, referencing object in tempdb.”

Today, let us quickly try to understand an error message as below.

“Database name ‘tempdb’ ignored, referencing object in tempdb.”.

Many of us would have got this message (I do prefer to call this as a warning message, not error message), however, we would not have noticed as it is not causing any fatal results. With this post, I would like to share my thoughts and like to have your views on this as well.

Let us first see when would you get this message?

use tempdb
GO
create Table #Temp_Table(Col1 int)
GO
Select * From tempdb..#Temp_Table

Now, interesting thing, when the query is changed a bit as below, the message is vanished.

Somehow, I was not convinced the above method as a solution, because that was actually against my understanding of 4 part naming convention (servername.databasename.schemaname.objectname). So, we further tried to test with few more combinations to understand how it works internally.

A simple query as below showed #Temp_Table is created with dbo schema.

As next step, tried to create a schema and a new object is created. If you look at the schema of the object, we can clearly see that it is associated with dbo schema not the new schema. That means, the objects created in tempdb database is always creating in dbo, not in any other schema. In fact, the schema part is actually ignoring for temp tables.

create schema testschema
GO
create Table testschema.#Temp_Table10(Col1 int)

Points to ponder

There is NO need of specifying schema for objects created in tempdb database.

Even we specify a schema name, SQL Server simply ignores the schema part.

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Errors and Exceptions, SQL

Error Message : The query processor ran out of internal resources and could not produce a query plan. This is a rare event and only expected for extremely complex queries or queries that reference a very large number of tables or partitions. Please simplify the query.
Error Message:
The query processor ran out of internal resources and could not produce a query plan. This is a rare event and only expected for extremely complex queries or queries that reference a very large number of tables or partitions. Please simplify the query. If you believe you have received this message in error, contact Customer Support Services for more information.

As specified in the error message, its a rare event or exception. The important message from the exception is that “Please simplify the query”. When the query is complex, the relational engine would not be able to create a query plan due to various reasons like the environment resource limitation, reduced capacity etc. and end up with the above exception.

The case I observed is with a dynamic query execution. I do not exactly going to give the query, however tries to provide a more like scenario. I wanted to create a dynamic query with an IN condition where the list of items are separated with a comma like below. 

declare @sql varchar(max)
Declare @values varchar(max)='val1','val2','val3'......'valhugenumber'
Select @sql = 'Select * from ' + @tablename + ' where ' + @columnname + ' in ('+@values+')'
Exec(@sql)


When executing this in one of environments (lower), the error is produced, however, the other interesting thing is its not happening in few other environments(eg. Production). As mentioned above, that is because it depends on the resources involved in various environment matters in producing the query plan.

Resolution:

From the analysis, the issue is associated with long (really long) list of values and when its parsing, the relational engine is not able to create a plan for the query execution. To resolve the issue, the query has been modified not to use the value list variable, instead populated those values into a temp table and then use the temp table as below. 

declare @sql varchar(max)
create table #temp (valuelist varchar(100))
Insert into #temp values('val1'),('val2'),('val3'),......('valhugenumber')
Select @sql = 'Select * from ' + @tablename + ' where ' + @columnname + ' in (Select valuelist from #temp)'
Exec(@sql)

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Errors and Exceptions, SQL

The data type ntext cannot be used as an operand to the UNION, INTERSECT or EXCEPT operators because it is not comparable.
Exception Message

With today’s post, we will deep dive into an error message that one of my friend encountered recently as below.
The data type ntext cannot be used as an operand to the UNION, INTERSECT or EXCEPT operators because it is not comparable.
Sample Code

Let us first replicate the issue with the below sample code snippet. 
Drop Table  if exists T1,T2
create Table T1(id int,Col1 ntext)
Create Table T2(id int,Col1 ntext)

Insert into T1 Values(1,'Big value')
Insert into T2 Values(1,'Big value')

Select  * From (
Select * From T1
union 
Select * From T2)A

The execution of the above code results in the error message and the message is very clear that those specified operators are not allowed with ntext datatype.

Solution

1. Avoid NTEXT datatype

NTEXT datatype is a deprecated datatype in SQL Server. Try to avoid in future development and replace the existing with nvarchar(max).

2. Replace UNION with UNION ALL (if possible)

UNION ALL is a clear winner of this situation over UNION operator. So, if you can change the code to replace union with union all, that would be the easiest way. Then why is it so? – Simple, UNION operator does a sort operation internally which is forbidden with datatype ntext whereas UNION ALL does not require sort operation. 

Select  * From (
Select * From T1
union ALL
Select * From T2)A

3. Construct column list without ntext datatype columns 

Drop Table  if exists T1,T2
create Table T1(id int,Col1 ntext)
Create Table T2(id int,Col1 ntext)

Insert into T1 Values(1,'Big value')
Insert into T2 Values(1,'Big value')

--Construction of column list without ntext datatype columns

Declare @Col_list varchar(max)
Set @Col_list = (
SELECT  STUFF((SELECT  ',' + name FROM sys.columns EE
            WHERE   EE.object_id =E.object_id and system_type_id not in (99)
            ORDER BY column_id 
        FOR XML PATH('')), 1, 1, '') AS 'CommaseparatedString'
FROM sys.columns E where object_id = object_id('T1') 
and system_type_id not in (99) group by object_id) 

Declare @sql nvarchar(max) = ''
Set @sql = 'Select  * From (
Select ' + @Col_list + ' From T1
union
Select ' + @Col_list + ' From T2)A'

exec sp_executesql @sql

Sometime, we may not be able to avoid the ntext column depending on the requirement. In such situation, you may use an explicit conversion of those ntext datatype to nvarchar(max) as below. 

--Construction of column list with ntext datatype columns but with explicit conversion of datatype

Declare @Col_list varchar(max)
Set @Col_list = (
SELECT  STUFF((SELECT  ',' + case when system_type_id= 99  then 'Cast(' +  name + ' as nvarchar(max)) as ' + name Else name End FROM sys.columns EE
            WHERE   EE.object_id =E.object_id 
            ORDER BY column_id 
        FOR XML PATH('')), 1, 1, '') AS 'CommaseparatedString'
FROM sys.columns E where object_id = object_id('T1') 
group by object_id)

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