cross database query only works one way MS SQL Server - sql

Question

I am attempting to insert data about index usage into a control database of sorts.. The query I am using is below.. the issue I have is that when I execute the query from the control database (lets call it A) it returns 0 results, but if I execute it from the source database (lets call that B) it runs just fine..
why?
This behavior is being seen on both SQL Server 2012 DEV and SQL Server 2008 EE.
Example 1 returns zero results:
USE A;
INSERT INTO A.dbo.UnusedIndexes
SELECT 
DB_NAME() AS DatabaseName
, SCHEMA_NAME(o.Schema_ID) AS SchemaName
, OBJECT_NAME(o.object_id) AS TableName
, ix.name AS IndexName
,((SUM(ps.used_page_count)over(partition by ix.index_id))*8)/1024 AS [IndexSizeMB]
, ix_usage_stats.user_updates
, ix_usage_stats.user_seeks + ix_usage_stats.user_scans + ix_usage_stats.user_lookups
AS [User_SeeksScansLookups]
    , ix_usage_stats.system_updates
, ix_usage_stats.system_seeks + ix_usage_stats.system_scans + ix_usage_stats.system_lookups
AS [System_SeeksScansLookups]
, NULL as [Drop_Statement]
, NULL as [Create_statement]
,getdate() as [date_added]
FROM B.sys.indexes ix
Left join B.sys.dm_db_index_usage_stats ix_usage_stats
 ON ix_usage_stats.object_id = ix.object_id
AND ix_usage_stats.index_id = ix.index_id
INNER JOIN B.sys.objects o ON ix.object_id = o.object_id
JOIN B.sys.dm_db_partition_stats ps ON ps.object_id = ix.object_id AND ix.index_id = ps.index_id
WHERE 
ix.name IS NOT NULL -- exclude heaps
AND ix.type <> 1 -- exclude the clustered indexes
AND o.is_ms_shipped = 0 -- exclude system objects
AND o.type NOT IN('F', 'UQ') -- exclude the foreign keys and unique contraints
AND SCHEMA_NAME(o.schema_id) not in ('dbo','stats', 'reporting') 
AND (ix_usage_stats.user_seeks = 0 or ix_usage_stats.user_seeks is NULL)
AND (ix_usage_stats.user_scans = 0 or ix_usage_stats.user_scans is null)
AND (ix_usage_stats.user_lookups = 0 or ix_usage_stats.user_lookups is null)
Example 2 returns the expected results, populating A.dbo.UnusedIndexes:
USE B;
INSERT INTO A.dbo.UnusedIndexes
SELECT
DB_NAME() AS DatabaseName
, SCHEMA_NAME(o.Schema_ID) AS SchemaName
, OBJECT_NAME(o.object_id) AS TableName
, ix.name AS IndexName
,((SUM(ps.used_page_count)over(partition by ix.index_id))*8)/1024 AS [IndexSizeMB]
, ix_usage_stats.user_updates
, ix_usage_stats.user_seeks + ix_usage_stats.user_scans + ix_usage_stats.user_lookups
AS [User_SeeksScansLookups]
, ix_usage_stats.system_updates
, ix_usage_stats.system_seeks + ix_usage_stats.system_scans + ix_usage_stats.system_lookups
AS [System_SeeksScansLookups]
, NULL as [Drop_Statement]
, NULL as [Create_statement]
,getdate() as [date_added]
FROM B.sys.indexes ix
Left join B.sys.dm_db_index_usage_stats ix_usage_stats
ON ix_usage_stats.object_id = ix.object_id
AND ix_usage_stats.index_id = ix.index_id
INNER JOIN B.sys.objects o ON ix.object_id = o.object_id
JOIN B.sys.dm_db_partition_stats ps ON ps.object_id = ix.object_id AND ix.index_id = ps.index_id
WHERE
ix.name IS NOT NULL -- exclude heaps
AND ix.type <> 1 -- exclude the clustered indexes
AND o.is_ms_shipped = 0 -- exclude system objects
AND o.type NOT IN('F', 'UQ') -- exclude the foreign keys and unique contraints
AND SCHEMA_NAME(o.schema_id) not in ('dbo','stats', 'reporting')
AND (ix_usage_stats.user_seeks = 0 or ix_usage_stats.user_seeks is NULL)
AND (ix_usage_stats.user_scans = 0 or ix_usage_stats.user_scans is null)
AND (ix_usage_stats.user_lookups = 0 or ix_usage_stats.user_lookups is null)
This works all day long:
USE A;
Select * from B.sys.indexes
Any help would be great - and unfortunately I am unable to execute this from database B, so the easy solution won't work.
Solved
Figured it out. the DB_NAME() was the issue. removing that and setting it to 'B' as databasename fixed the issue.

Answer 1

Try using sp_executesql from the target database:
USE A;
INSERT INTO A.dbo.UnusedIndexes
EXEC B.sys.sp_executesql N'
SELECT DB_NAME() AS DatabaseName
,SCHEMA_NAME(o.Schema_ID) AS SchemaName
,OBJECT_NAME(o.object_id) AS TableName
,ix.NAME AS IndexName
,((SUM(ps.used_page_count) OVER (PARTITION BY ix.index_id)) * 8) / 1024 AS [IndexSizeMB]
,ix_usage_stats.user_updates
,ix_usage_stats.user_seeks + ix_usage_stats.user_scans + ix_usage_stats.user_lookups AS [User_SeeksScansLookups]
,ix_usage_stats.system_updates
,ix_usage_stats.system_seeks + ix_usage_stats.system_scans + ix_usage_stats.system_lookups AS [System_SeeksScansLookups]
,NULL AS [Drop_Statement]
,NULL AS [Create_statement]
,getdate() AS [date_added]
FROM sys.indexes ix
LEFT JOIN sys.dm_db_index_usage_stats ix_usage_stats
ON ix_usage_stats.object_id = ix.object_id
AND ix_usage_stats.index_id = ix.index_id
INNER JOIN sys.objects o
ON ix.object_id = o.object_id
JOIN sys.dm_db_partition_stats ps
ON ps.object_id = ix.object_id
AND ix.index_id = ps.index_id
WHERE 1 = 1
AND ix.name IS NOT NULL -- exclude heaps
AND ix.type <> 1 -- exclude the clustered indexes
AND o.is_ms_shipped = 0 -- exclude system objects
AND o.type NOT IN(''F'', ''UQ'') -- exclude the foreign keys and unique contraints
AND SCHEMA_NAME(o.schema_id) not in (''dbo'',''stats'', ''reporting'')
AND (
ix_usage_stats.user_seeks = 0
OR ix_usage_stats.user_seeks IS NULL
)
AND (
ix_usage_stats.user_scans = 0
OR ix_usage_stats.user_scans IS NULL
)
AND (
ix_usage_stats.user_lookups = 0
OR ix_usage_stats.user_lookups IS NULL
)
'