TryCatchFinally.net Some SQL, some .NET, and whatever else

18Mar/130

Unexpected results from ISNULL in SQL Compact 3.5

In SQL Server, the ISNULL function takes two arguments - the first is a potentially NULL value, and the second is another potentially NULL value. If the first value is NULL, the function returns the second value instead. It's always been this way - for example:

  SELECT V1, V2,
         ISNULL(V1, V2) as [Result],
         Descr
  FROM (SELECT 10 as V1, 20 as V2, 'Returns first' as Descr UNION
        SELECT 10 as V1, NULL as V2, 'Returns first' as Descr UNION
        SELECT NULL as V1, 20 as V2, 'Returns second' as Descr UNION
        SELECT NULL as V1, NULL as V2, 'Both NULL - return NULL' as Descr) t

In SQL Server, you get the following results:

V1      V2      Result  Descr
10      20      10      Returns first
10      NULL    10      Returns first
NULL    20      20      Returns second
NULL    NULL    NULL    Both NULL - return NULL

However, SQL Compact implements ISNULL differently, in a way that's not compatible at all - instead, the ISNULL function returns a 0 or 1 based on whether the first parameter is NULL! It doesn't even process the second parameter, but instead of failing with an "Invalid Syntax" error, it happily accepts it, executes, and returns unexpected results. In SQL Compact, you get the following result set:

V1      V2      Result  Descr
10      20      0       Returns first
10      NULL    0       Returns first
NULL    20      1       Returns second
NULL    NULL    1       Both NULL - return NULL

Notice the difference? The ISNULL column is returning the value based only on the first parameter (a "0" if it's not NULL, and a "1" if it is), and if you're not expecting it, it silently mis-calculates any formulas containing that function. If you're relying on the function in any statements that add values together or make decisions based on the results, you're in for some very expected behavior (in my case, I noticed totals that were wildly incorrect).

As an alternative, you should be using the COALESCE - it accepts multiple parameters and it walks down the list until it finds one that's not null, returning a NULL value if all parameters are NULL. This function can be used in place of ISNULL in SQL Server code with exactly the same behavior (i.e. no changes), and as a bonus, it acts the same in SQL Compact, so your formulas will work properly there as well. The example above becomes:

  SELECT V1, V2,
         COALESCE(V1, V2) as [Result],
         Descr
  FROM (SELECT 10 as V1, 20 as V2, 'Returns first' as Descr UNION
        SELECT 10 as V1, NULL as V2, 'Returns first' as Descr UNION
        SELECT NULL as V1, 20 as V2, 'Returns second' as Descr UNION
        SELECT NULL as V1, NULL as V2, 'Both NULL - return NULL' as Descr) t

And on both SQL Server and SQL Compact, the result set is the same:

V1      V2      Result  Descr
10      20      10      Returns first
10      NULL    10      Returns first
NULL    20      20      Returns second
NULL    NULL    NULL    Both NULL - return NULL

+1 for consistency!

MORAL of the story:

When executing statements on different platforms, ensure the functions you use behave in the same manner on both - and even when considering multiple platforms from the same vendor, named almost identically, don't assume things behave unless you've tested them 🙂

10Mar/130

“Initializing Reconciler has failed” when setting up SQL Compact replication

When initializing replication to a .NET Compact Framework client on a mobile device, I was receiving an error message when I attempted to start the synchronize:

Initializing the SQL Server Reconciler has failed. Try again.

I had confirmed that SQL Compact web replication was set up correctly, and checking the URL came back as expected. Searching for the error online comes back with a dozen recommendations, but when I traced the replication sync attempt, I saw the following statement executed:

exec sp_helpdistpublisher N'SQLSERVERNAME'

Followed immediately by the error message:

The remote server "SQLSERVERNAME" does not exist, or has not been designated as a valid Publisher, or you may not have permission to see available Publishers.

Sure enough, executing that command in SSMS, logged in as my replication user, gave me the same error message. At some point, I'd changed the user I was using to set up the subscription, and that user didn't have rights to view the publication list on my SQL Server. The fix was pretty easy:

  1. In SQL Management Studio, right-click the publication
  2. Select "Properties" and then open the "Publication Access List" tab
  3. Add the user you're connecting your subscriber with to this list

Here's a shot of the screen where I had to make this change, in case there's any confusion:

Publication Security Settings

2Mar/130

Refreshing changed .NET SQL CLR assemblies after patching/updates

After applying some Windows updates to one of my servers, I started getting the following error when I ran a customer .NET SQL-CLR stored proc:

Server: Msg 6522, Level 16, State 2, Line 1
A .NET Framework error occurred during execution of user defined routine or aggregate 'somemethodyourecalling':

System.IO.FileLoadException: Could not load file or assembly 'System.Drawing, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. Assembly in host store has a different signature than assembly in GAC. (Exception from HRESULT: 0x80131050)

I'd imported some additional assemblies into SQL Server for use in SQL CLR mapped stored procedures, and the Windows updates had included a service pack for .NET, which changed some of the assemblies. Now the version I'd linked to SQL Server no longer existed on disk, and SQL couldn't load it - that made sense, and is documented pretty clearly in this MS Support article: http://support.microsoft.com/kb/949080

However, I had dozens of servers with SQL CLR components enabled, and hundreds of different assemblies loaded across them all, and not always the same in each server, so a standard update script wouldn't work to refresh all the changed assemblies (the MS Support link provides a list of the standard ones that cause that error, but if you've got custom assemblies loaded, or you've loaded an assembly that's not specifically cleared for SQL CLR, then it's not on the list either). To deal with this, I wrote a script that fetches the assembly list for a database and attempts to refresh every one of them from their disk location. If they haven't changed, the update attempt will fail with a specific error message about the MVID, and there's no change for that assembly.

Also, I've commented out the line that restricts it to just framework assemblies (System.* and Microsoft.*), but you can uncomment that line if you'd like to restrict the refresh from attempting to reload your custom assemblies as well.

DECLARE @AssemblyName VARCHAR(255),
	    @AssemblyLocation VARCHAR(255),
	    @AlterAssemblyCommand NVARCHAR(1024),
	    @DotNetFolder VARCHAR(100)

   SET @DotNetFolder = 'C:\Windows\Microsoft.NET\Framework\v2.0.50727'

CREATE TABLE #Results (
		AssemblyName VARCHAR(255),
		AssemblyLocation VARCHAR(255),
		AlterAssemblyCommand NVARCHAR(1024),
		Results VARCHAR(1024)
)

select sa.name as AssemblyName,
		saf.name as Assemblylocation,
		case when charindex('', saf.name) = 0
			then 'ALTER ASSEMBLY [' + sa.name + '] FROM ''' + @DotNetFolder
			else 'ALTER ASSEMBLY [' + sa.name + '] FROM '''
		end + saf.name + (case right(saf.name, 4) when '.dll' then '' else '.dll' end) + ''''
		as AlterAssemblyCommand
INTO #Refresh
from sys.assemblies sa
join sys.assembly_files saf
  on sa.assembly_id = saf.assembly_id
where sa.name <> ('Microsoft.SqlServer.Types')
  --and (sa.name like 'System.%' or sa.name like 'microsoft.%')

DECLARE Commands CURSOR FAST_FORWARD FOR
SELECT AssemblyName,
	   AssemblyLocation,
	   AlterAssemblyCommand
  FROM #Refresh

OPEN Commands

FETCH NEXT FROM Commands
INTO @AssemblyName,
	   @AssemblyLocation,
	   @AlterAssemblyCommand

WHILE @@FETCH_STATUS = 0
BEGIN

	BEGIN TRY
		exec sp_executesql @AlterAssemblyCommand

		insert into #Results
		SELECT @AssemblyName,
				@AssemblyLocation,
				@AlterAssemblyCommand,
				'Assembly refreshed successfully'

	END TRY
	BEGIN CATCH

		insert into #Results
		SELECT @AssemblyName,
				@AssemblyLocation,
				@AlterAssemblyCommand,
				CASE ERROR_NUMBER()
					WHEN 6285 THEN 'No update necessary (MVID match)'
					WHEN 6501 THEN 'Physical assembly not found at specified location (SQL Error 6501)'
					ELSE ERROR_MESSAGE() + ' (SQL Error ' + convert(varchar(10), ERROR_NUMBER()) + ')'
				END

	END CATCH

	FETCH NEXT FROM Commands
	INTO @AssemblyName,
		   @AssemblyLocation,
		   @AlterAssemblyCommand

END

CLOSE Commands
DEALLOCATE Commands

SELECT * FROM #Results

drop table #refresh
drop table #Results

While troubleshooting the error, I came across this as well - I don't have a SQL 2012 server handy to check with, it looks like this problem might be resolved with a reboot in SQL 2012:

http://msdn.microsoft.com/en-us/library/hh479773.aspx

I'm not sure if that's the case, but it would make things easier. Also, it would be nice if there was some kind of "ALTER ASSEMBLY [SomeAssembly] REFRESH" command to address this problem, but maybe in a future version.

Additionally, this error can be caused if the signing of an assembly has changed, but not necessarily the signature, but just reloading it from disk won't work because the method that SQL Server uses to determine if there's been a change is the MVID, and that doesn't change unless there's been a code change of some kind (see the Connect bug here). In those cases, you'll actually need to drop and recreate the assembly, including any supporting objects that rely on that assembly.