How to select info about indexes with specified columns from all databases in the instance using TSQL? This query selects all the indexes - its names, fragmentation, and some other parameters from the current database. 

select
    idx.[name] as [index_name],
    sc.[name] as [schema_name],
    obj.[name] as [table_name],  
    ips.[avg_fragmentation_in_percent] as [fragmentation_percent]
from sys.indexes as idx
inner join sys.objects as obj on idx.object_id = obj.object_id
inner join sys.schemas as sc  on obj.schema_id = sc.schema_id
cross apply sys.dm_db_index_physical_stats( DB_ID(), idx.object_id, idx.index_id, NULL ,'LIMITED') AS ips
where idx.[name] is not NULL 
order by [fragmentation_percent] desc;


Now I need to select all the indexes with specified columns from all databases. I can use USE [dbname] when I execute the statement manually, but I need to put it in a cursor, so I cannot write USE [dbname] in a cursor. 

How can I substitute the database selection in the ...CROSS APPLY sys.dm_db_index_physical_stats( DB_ID(), ... part of my statement?

Help will be much appreciated to show how can I select all database indexes with a single query.

Something like this:

declare cr_index cursor
for
exec(@dynamicUSE)
select
    idx.[name] as [index_name],
    sc.[name] as [schema_name],
    obj.[name] as [table_name],  
    ips.[avg_fragmentation_in_percent] as [fragmentation_percent]
from sys.indexes as idx
inner join sys.objects as obj on idx.object_id = obj.object_id
inner join sys.schemas as sc  on obj.schema_id = sc.schema_id
cross apply sys.dm_db_index_physical_stats( DB_ID(), idx.object_id, idx.index_id, NULL ,'LIMITED') AS ips
where idx.[name] is not NULL 
order by [fragmentation_percent] desc;
You can do dynamic SQL in a cursor to do it on every database on the server that way : 

DECLARE @DB_Name varchar(100) 
DECLARE @Command nvarchar(1000)
DECLARE database_cursor CURSOR FOR 
SELECT name FROM MASTER.sys.sysdatabases 

OPEN database_cursor

FETCH NEXT FROM database_cursor INTO @DB_Name

WHILE @@FETCH_STATUS = 0 
BEGIN 
 SELECT @Command = 'USE [' +  @DB_Name + '];  select
   idx.[name] as [index_name],
   sc.[name] as [schema_name],
   obj.[name] as [table_name],  
   ips.[avg_fragmentation_in_percent] as [fragmentation_percent]
from sys.indexes as idx
inner join sys.objects as obj on idx.object_id = obj.object_id
inner join sys.schemas as sc  on obj.schema_id = sc.schema_id
cross apply sys.dm_db_index_physical_stats( DB_ID(), idx.object_id, idx.index_id, NULL ,''LIMITED'') AS ips
where idx.[name] is not NULL 
order by [fragmentation_percent] desc;'
 EXEC sp_executesql @Command

 FETCH NEXT FROM database_cursor INTO @DB_Name 
END

CLOSE database_cursor 
DEALLOCATE database_cursor