How to identify duplicate indexes along with columns in SQL Server?

To get the key column list from indexes that are duplicates in SQL Server, you can use the following query:

use databasename
go

WITH DuplicateIndexes AS (
    SELECT 
        i.OBJECT_ID,
        i.index_id
    FROM 
        sys.index_columns ic
    JOIN 
        sys.indexes i ON i.OBJECT_ID = ic.OBJECT_ID 
                     AND i.index_id = ic.index_id
    WHERE 
        i.type_desc <> 'HEAP' 
		AND OBJECT_NAME(i.OBJECT_ID) NOT LIKE '%sys%' --excluding system tables
    GROUP BY 
        i.OBJECT_ID, i.index_id
    HAVING 
        COUNT(*) > 1 -- to check duplicates 
)

SELECT 
    SCHEMA_NAME(o.schema_id) AS SchemaName,
    OBJECT_NAME(ic.OBJECT_ID) AS TableName,
    i.name AS IndexName,
    STRING_AGG(c.name, ', ') WITHIN GROUP (ORDER BY ic.key_ordinal) AS IndexedColumns
FROM 
    sys.index_columns ic
JOIN 
    sys.indexes i ON i.OBJECT_ID = ic.OBJECT_ID 
                 AND i.index_id = ic.index_id
JOIN 
    sys.objects o ON o.OBJECT_ID = ic.OBJECT_ID
JOIN 
    sys.columns c ON ic.OBJECT_ID = c.OBJECT_ID 
                 AND ic.column_id = c.column_id
JOIN 
    DuplicateIndexes di ON di.OBJECT_ID = ic.OBJECT_ID 
                        AND di.index_id = ic.index_id
GROUP BY 
    o.schema_id, ic.OBJECT_ID, i.name;
  

This query first identifies the indexes that are duplicates, and then retrieves the table name, index name, and the key column list for each duplicate index.

Execute this query in your SQL Server management tool to get the key column list from indexes that are duplicates in your database.