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sys.dm_db_missing_index_columns (Transact-SQL)

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Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

Returns information about database table columns that are missing an index. sys.dm_db_missing_index_columns is a dynamic management function.

Syntax

sys.dm_db_missing_index_columns(index_handle)

Arguments

index_handle
An integer that uniquely identifies a missing index. It can be obtained from the following dynamic management objects:

sys.dm_db_missing_index_details (Transact-SQL)

sys.dm_db_missing_index_groups (Transact-SQL)

Table Returned

Column name Data type Description
column_id int ID of the column.
column_name sysname Name of the table column.
column_usage varchar(20) How the column is used by the query. The possible values and their descriptions are:

EQUALITY: Column contributes to a predicate that expresses equality, of the form:
table.column = constant_value

INEQUALITY: Column contributes to a predicate that expresses inequality, for example, a predicate of the form: table.column > constant_value. Any comparison operator other than "=" expresses inequality.

INCLUDE: Column is not used to evaluate a predicate, but is used for another reason, for example, to cover a query.

Remarks

Information returned by sys.dm_db_missing_index_columns is updated when a query is optimized by the query optimizer, and is not persisted. Missing index information is kept only until the database engine is restarted. Database administrators should periodically make backup copies of the missing index information if they want to keep it after server recycling. Use the sqlserver_start_time column in sys.dm_os_sys_info to find the last database engine startup time.

Transaction Consistency

If a transaction creates or drops a table, the rows containing missing index information about the dropped objects are removed from this dynamic management object, preserving transaction consistency.

Permissions

Users must be granted the VIEW SERVER STATE permission or any permission that implies the VIEW SERVER STATE permission to query this dynamic management function.

Permissions for SQL Server 2022 and later

Requires VIEW SERVER PERFORMANCE STATE permission on the server.

Examples

The following example runs a query against the Address table and then runs a query using the sys.dm_db_missing_index_columns dynamic management view to return the table columns that are missing an index.

USE AdventureWorks2022;  
GO  
SELECT City, StateProvinceID, PostalCode  
FROM Person.Address  
WHERE StateProvinceID = 9;  
GO  
SELECT mig.*, statement AS table_name,  
    column_id, column_name, column_usage  
FROM sys.dm_db_missing_index_details AS mid  
CROSS APPLY sys.dm_db_missing_index_columns (mid.index_handle)  
INNER JOIN sys.dm_db_missing_index_groups AS mig ON mig.index_handle = mid.index_handle  
ORDER BY mig.index_group_handle, mig.index_handle, column_id;  
GO

Missing index suggestions should be combined when possible with one another, and with existing indexes in the current database. Learn how to apply these suggestions in tune nonclustered indexes with missing index suggestions.

Next steps

Learn more about the missing index feature in the following articles: