Missing Indexes

-- Source: "SQL Server Diagnostic Information Queries" by Glenn Berry (altered) – https://glennsqlperformance.com/resources/
-- Copyright (C) Glenn Berry. All rights reserved.
-- You may alter this code for your own *non-commercial* purposes. You may republish altered code as long as you include this copyright and give due credit.
-- THIS CODE AND INFORMATION ARE PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.

SELECT CONVERT(decimal(18,2), migs.user_seeks * migs.avg_total_user_cost * (migs.avg_user_impact * 0.01)) AS [index_advantage],
FORMAT(migs.last_user_seek, 'yyyy-MM-dd HH:mm:ss') AS [last_user_seek], mid.[statement] AS [Database.Schema.Table],
COUNT(1) OVER(PARTITION BY mid.[statement]) AS [missing_indexes_for_table],
COUNT(1) OVER(PARTITION BY mid.[statement], mid.equality_columns) AS [similar_missing_indexes_for_table],
mid.equality_columns, mid.inequality_columns, mid.included_columns, migs.user_seeks, 
CONVERT(decimal(18,2), migs.avg_total_user_cost) AS [avg_total_user_cost], migs.avg_user_impact 
FROM sys.dm_db_missing_index_group_stats AS migs WITH (NOLOCK)
INNER JOIN sys.dm_db_missing_index_groups AS mig WITH (NOLOCK)
ON migs.group_handle = mig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details AS mid WITH (NOLOCK)
ON mig.index_handle = mid.index_handle
ORDER BY index_advantage DESC OPTION (RECOMPILE);
------

-- Getting missing index information for all of the databases on the instance is very useful
-- Look at last user seek time, number of user seeks to help determine source and importance
-- Also look at avg_user_impact and avg_total_user_cost to help determine importance
-- SQL Server is overly eager to add included columns, so beware
-- Do not just blindly add indexes that show up from this query!!!
-- Håkan Winther has given me some great suggestions for this query