How to get Information about indexes of system views

How I can get information about indexes of system views.

I write 开发者_运维知识库this query and look at execution plan.I saw it used Index scan rather Index seek.Any one know why?

SELECT OBJECT_NAME(OBJECT_ID) TableName, st.row_count
 FROM sys.dm_db_partition_stats st
 WHERE index_id < 2 AND OBJECT_NAME(OBJECT_ID)='Mytbl'

select i.name  as idx_name,
       i.type_desc,
       i.is_unique,
       ac.name as col_name,
       c.key_ordinal,
       c.is_descending_key,
       c.is_included_column
from   sys.indexes i
       join sys.all_objects a
         on a.object_id = i.object_id
       join sys.index_columns c
         on c.object_id = i.object_id
            and c.index_id = i.index_id
       join sys.all_columns ac
         on ac.object_id = i.object_id
            and c.column_id = ac.column_id
where  a.name = 'sysidxstats'  

Returns

idx_name          type_desc       is_unique col_name    key_ordinal is_descending_key is_included_column
----------------- --------------- --------- ----------- ----------- ----------------- ------------------
clst              CLUSTERED       1         id          1           0                 0
clst              CLUSTERED       1         indid       2           0                 0
nc                NONCLUSTERED    1         name        1           0                 0
nc                NONCLUSTERED    1         id          2           0                 0

Use

SELECT OBJECT_NAME(object_id) TableName,
       st.row_count
FROM   sys.dm_db_partition_stats st
WHERE  index_id < 2
       AND object_id = OBJECT_ID('Mytbl')  

To get an index seek.

WHERE OBJECT_NAME(object_id)='Mytbl' is not a seekable predicate.

Check out this post http://blog.sqlauthority.com/2009/08/24/sql-server-index-seek-vs-index-scan-diffefence-and-usage-a-simple-note/ it doesn't talk about how to get index info from system views but it does explain why reasons why an Index Scan may be used over an Index Seek.