sys.dm_db_missing_index_details
New: 5 December 2005
Returns detailed information about missing indexes.
| Column name | Data type | Description |
|---|---|---|
index_handle |
int |
Identifies a particular missing index. The identifier is unique across the server. index_handle is the key of this table. |
database_id |
smallint |
Identifies the database where the table with the missing index resides. |
object_id |
int |
Identifies the table where the index is missing. |
equality_columns |
nvarchar(4000) |
Comma-separated list of columns that contribute to equality predicates of the form: table.column = |
inequality_columns |
nvarchar(4000) |
Comma-separated list of columns that contribute to inequality predicates, for example, predicates of the form: table.column > constant_value Any comparison operator other than "=" expresses inequality. For a complete list of comparison operators, see Comparison Operators (Database Engine). |
included_columns |
nvarchar(4000) |
Comma-separated list of columns needed as covering columns for the query. For more information about covering or included columns, see Creating Indexes with Included Columns. |
statement |
nvarchar(4000) |
Name of the table where the index is missing. |
Remarks
Information returned by sys.dm_db_missing_index_details is updated when a query is optimized by the query optimizer, and is not persisted. Missing index information is kept only until SQL Server is restarted. Database administrators should periodically make backup copies of the missing index information if they want to keep it after server recycling.
To determine which missing index groups a particular missing index is part of, you can query the sys.dm_db_missing_index_groups dynamic management view by equijoining it with sys.dm_db_missing_index_details based on the index_handle column.
For information about enabling and disabling missing index information collection, see About the Missing Indexes Feature.
For information about limitations of this feature, see Limitations for Using the Missing Indexes Feature.
Using Missing Index Information in CREATE INDEX Statements
To convert the information returned by sys.dm_db_missing_index_details into a CREATE INDEX statement, equality columns should be put before the inequality columns, and together they should make the key of the index. Included columns should be added to the CREATE INDEX statement using the INCLUDE clause. To determine an effective order for the equality columns, order them based on their selectivity: list the most selective columns first (leftmost in the column list). For more information about writing CREATE INDEX statements using the missing index information returned by sys.dm_db_missing_index_details, see Using Missing Index Information to Write CREATE INDEX Statements.
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. For more information about transaction consistency in relation to the missing indexes dynamic management objects, see About the Missing Indexes Feature.
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 view.
See Also
Reference
sys.dm_db_missing_index_columns
sys.dm_db_missing_index_groups
sys.dm_db_missing_index_group_stats
Other Resources
About the Missing Indexes Feature