13.5.1 Number of rows and their output order in the summary information for indexes
One row of summary information is output for each index. The number of rows output equals the number of indexes for which summary information has been obtained. Title lines (column header rows) are not included in the row count.
The rows are output in ascending order of the DB area IDs. Rows with the same DB area ID are output in ascending order of the index names (schema-name.index-identifier).