SELECT OBJECT_NAME(ic.object_id) AS Таблица, SUM(sys.columns.max_length) AS [ДлинаИндекса], i.name AS Индекс
FROM sys.indexes AS i INNER JOIN
sys.index_columns AS ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id INNER JOIN
sys.columns ON ic.column_id = sys.columns.column_id AND ic.object_id = sys.columns.object_id
GROUP BY OBJECT_NAME(ic.object_id), i.name, sys.columns.name
ORDER BY [ДлинаИндекса] DESC