sys.dm_db_index_physical_stats shows I have 3 PK indexes after rebuild

Question

I was checking the fragmentation in the index in one table of my DB with the following query

SELECT a.object_id, object_name(a.object_id) AS TableName,
    a.index_id, name AS IndedxName, avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats
    (DB_ID (N'prod-db')
        , OBJECT_ID(N'[dbo].[Channel]')
        , NULL
        , NULL
        , NULL) AS a
INNER JOIN sys.indexes AS b
    ON a.object_id = b.object_id
    AND a.index_id = b.index_id;
GO

And discovered that it listed PK_Channel 3 times,

TableName	index_id	IndedxName	object_id	avg_fragmentation_in_percent
Channel	1	PK_Channel	1557580587	0,01
Channel	1	PK_Channel	1557580587	0
Channel	1	PK_Channel	1557580587	0
Channel	3	idx_Channel_RegisteredTime	1557580587	0,0429737859905458

I have rebuilt the index 2 times, so it coincides with that. But is this a good thing? Or is this normal (aka expected behaviour)? Should I "fix" this? if so, how?

It is worth noting that the index idx_Channel_RegisteredTime was rebuilt once and no duplication was found in sys.dm_db_index_physical_stats . Can anyone shed light on this?

Also please notice that when I list the indexes in the Management Studio it only shows PK_Channel once, which is what I would expect.

In case it makes any difference or any one is curious, I rebuilt the indexes using the following statement

ALTER INDEX PK_Channel ON [dbo].[Channel]
REBUILD
;

ALTER INDEX idx_Channel_RegisteredTime ON [dbo].[Channel]
REBUILD
;

Thanks

Answer 1

You only have one index, with multiple levels in the B-tree.

From the docs for sys.dm_db_index_physical_stats :

For an index, one row is returned for each level of the B-tree in each partition.

This means that dm_db_index_physical_stats will return a row for each level of the B-tree. You are joining that onto the single row from sys.indexes .