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Editorial Team
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Asked: 2026-05-25T15:17:48+00:00

I found the following SQL intended to help identify missing indexes. I’d like to

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I found the following SQL intended to help identify missing indexes. I’d like to better understand the output.

   SELECT   migs.avg_total_user_cost * (migs.avg_user_impact / 100.0) * (migs.user_seeks + migs.user_scans) AS ExpectedImprovement
           , DB_NAME(mid.database_id)            AS DBName
           , mid.[object_id]                     AS ObjectID
           , mid.statement                       AS FullyQualifiedObjectName
           , ISNULL (mid.equality_columns,'') +
             CASE WHEN mid.equality_columns IS NOT NULL AND mid.inequality_columns IS NOT NULL THEN
                ','
             ELSE
                ''
             END +
             ISNULL (mid.inequality_columns, '') AS IndexColumns
           , ISNULL (mid.included_columns, '') AS IncludeColumns
           , migs.user_seeks
           , migs.user_scans
           , migs.last_user_seek
           , migs.last_user_scan
      FROM sys.dm_db_missing_index_groups      mig
INNER JOIN sys.dm_db_missing_index_group_stats migs ON migs.group_handle = mig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details     mid  ON mig.index_handle = mid.index_handle
     WHERE migs.avg_total_user_cost * (migs.avg_user_impact / 100.0) * (migs.user_seeks + migs.user_scans) > 10
  ORDER BY migs.avg_total_user_cost * migs.avg_user_impact * (migs.user_seeks + migs.user_scans) DESC

One of the returned columns is “Include Columns”.

I was wondering if this meant that the column names mentioned should be added to the list of columns in the index or whether there is some other feature to return those presumably high accessed column value without adding them to the index itself. (Perhaps I imagined hearing of such a feature or maybe it was another vendor’s db)

Is the output just suggesting that the list of columns in the index be expanded by the columns mentioned in the “Include Columns” returned value? I am reacting to output suggesting that I add 15 fields to an index and this seems potentially excessive to me.

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1 Answer

  1. Editorial Team

    SQLServers lets you “include” non-key columns (See details here). The main difference between key columns and non-key columns in the index is that non-key columns are stored only in the leaf level of the index in contrast to key columns which are stored at all levels.

    I wouldn’t recommend to follow advise of your script output (your script is good, don’t get me wrong) literally, i.e. you don’t really have to create all the suggested indexes and include all the columns it wants from you. From my experience SQLServer wants you to make all your query to have a covering index which may affect performance of update/insert and increase database size.

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