To analyze further, the following query can be used to find out which indexes don’t have clustered indexes defined:

WITH CTE_1
AS
(
SELECT db_name() as dbname,
o.name as tablename,
(SELECT SUM(p.rows)
FROM sys.partitions p
WHERE p.index_id = i.index_id
AND i.object_id = p.object_id) as number_of_rows
FROM sys.indexes i
INNER JOIN sys.objects o
ON i.object_id = o.object_id
WHERE OBJECTPROPERTY(o.object_id, 'IsUserTable') = 1
AND OBJECTPROPERTY(o.object_id, 'TableHasClustIndex') = 0
)
SELECT *
FROM CTE_1
WHERE number_of_rows > 1000;