Category: Errors and Exceptions

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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Errors and Exceptions, SQL

SQL Server – Invalid Urn filter on server level: filter must be empty, or server attribute must be equal with the true server name

Problem Statement:

One of my colleague has reported an issue as below while he is trying to restore a database from backup.

SQL Server – Invalid Urn filter on server level: filter must be empty, or server attribute must be equal with the true server name

To my best knowledge, I was seeing this error first time and I was trying to understand about the issue with my google search and there are quite few good posts out there too.

http://blog.patricknielsen.net/2011/01/sql-server-invalid-urn-filter-on-server.html
https://debabratahowlee.blogspot.com/2016/09/sql-server-invalid-urn-filter-on-server.html

But somehow I was thinking something different as I was sure there were no activities at server level. Then I simply closed all open connections and restarted SSMS and tried and it worked perfectly this time. So, I do not have any clue yet what would have happened under the cover, however, am sure there is something gone bad it could be a failover/underlined network or anything that it could not resolve the server name.

If you have any different thoughts, please share in comment section.

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Errors and Exceptions, SQL

Error: Changes to the state or options of database ‘dbname’ cannot be made at this time. The database is in single-user mode, and a user is currently connected to it.
One of my colleague had an issue in dropping a database in her testing environment. She was not able to drop a database as she gets an error message (as below). Let me try to provide what she tried and ended up for every ones understanding. 
alter database [dbname] set multi_user with rollback immediate
Drop database [dbname]

Error Message:

Msg 5064, Level 16, State 1, Line 1 Changes to the state or options of database ‘dbname’ cannot be made at this time. The database is in single-user mode, and a user is currently connected to it. Msg 5069, Level 16, State 1, Line 1 ALTER DATABASE statement failed.

Solution:

When I analysed, I could find that the database has gone into single user mode and there was an open session on this database.Since, its a testing environment, I had killed the open session from the database and tried to drop the database by putting it multi user as first step as below and it was successful. 

USE master;

DECLARE @killSessions varchar(8000) = '';  
SELECT @killSessions = @killSessions + 'kill ' + CONVERT(varchar(5), spid) + ';'  
FROM master..sysprocesses  
WHERE dbid = db_id('dbname')
EXEC(@killSessions); 

alter database [dbname] set multi_user with rollback immediate
--Drop database [dbname] /*Only if need to be dropped*/

Hope this helps if you come across similar situations.

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