Get Read-to-Write Ratio for All Indexes

Here's a quick script to help you quantify how useful your indexes are, in the sense of how much they're used to speed up queries, compared to how much work it is for SQL Server to maintain them during inserts, updates, and deletes. This only reflects the usage since the last SQL Server boot.

-- Displays the read-to-update ratio of all indexes.  Good for finding ones that may not be needed.
DECLARE @dbid INT = DB_ID(DB_NAME())

; WITH cteUser AS
(
    SELECT object_id,
           index_id,
           user_seeks + user_scans + user_lookups   AS 'User Reads',
           user_updates                             AS 'User Updates'
      FROM sys.dm_db_index_usage_stats   
     WHERE database_id = @dbid
)
,
cteSystem AS
(
    SELECT object_id,
           index_id,
           system_seeks + system_scans + system_lookups   AS 'System Reads',
           system_updates                                 AS 'System Updates'
      FROM sys.dm_db_index_usage_stats   
     WHERE database_id = @dbid
)
,
cteTotal AS
(
    SELECT u.object_id,
           u.index_id,
           [User Reads]   + [System Reads]     AS 'Total Reads',
           [User Updates] + [System Updates]   AS 'Total Updates'
      FROM cteUser     u
      JOIN cteSystem   s
        ON u.object_id = s.object_id
       AND u.index_id  = s.index_id
)
,
cteReadToUpdateRatio AS
(
    SELECT object_id,
           index_id,
           CONVERT(NVARCHAR,
                  CONVERT(MONEY, ISNULL(
                                        CAST([Total Reads] AS REAL)
                                        /
                                        NULLIF([Total Updates], 0.0)
                                        , [Total Reads]
                                        )
                               , 1
                         )
                  )   AS 'Read-to-Update Ratio'
                  
      FROM cteTotal
)
SELECT OBJECT_SCHEMA_NAME(i.object_id)                                                                  AS 'Schema Name',
       OBJECT_NAME(i.object_id)                                                                         AS 'Table Name',
       i.name                                                                                           AS 'Index Name',
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, u.[User Reads]),                      1), '.00', '')    AS 'User Reads',                   
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, u.[User Updates]),                    1), '.00', '')    AS 'User Updates',                 
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, s.[System Reads]),                    1), '.00', '')    AS 'System Reads',                 
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, s.[System Updates]),                  1), '.00', '')    AS 'System Updates',               
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, t.[Total Reads]),                     1), '.00', '')    AS 'Total Reads',                
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, t.[Total Updates]),                   1), '.00', '')    AS 'Total Updates',                
                                                r.[Read-to-Update Ratio]                                AS 'Read-to-Update Ratio',         
       REPLACE(CONVERT(NVARCHAR, CONVERT(MONEY, t.[Total Reads] + t.[Total Updates]), 1), '.00', '')    AS 'Total Reads + Total Updates'
  FROM cteUser                        u
  JOIN cteSystem                      s
    ON u.object_id = s.object_id
   AND u.index_id  = s.index_id
  JOIN cteTotal                       t
    ON u.object_id = t.object_id
   AND u.index_id  = t.index_id
  JOIN cteReadToUpdateRatio           r
    ON u.object_id = r.object_id
   AND u.index_id  = r.index_id
  JOIN sys.indexes                    i
    ON u.object_id = i.object_id
   AND u.index_id  = i.index_id
  JOIN sys.objects                    o
    ON u.object_id = o.object_id
 WHERE OBJECTPROPERTY(o.object_id, 'IsUserTable') = 1
   AND i.is_primary_key = 0
 ORDER BY CAST(r.[Read-to-Update Ratio] AS REAL)

The results appear in "least useful" index first. Be sure to read and test this script before using in a Production environment.