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Clustered and non-clustered indexes - IBM Documentation

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Index architectures are classified as clustered or non-clustered. Clustered indexes are indexes whose order of the rows in the data pages corresponds to the order of the rows in the index. This order is why only one clustered index can exist in any table, whereas, many non-clustered indexes can exist in the table. In some database systems, the leaf node of the clustered index corresponds to the actual data, not a pointer to data that is found elsewhere. Both clustered and non-clustered indexes contain only keys and record identifiers in the index structure. The record identifiers always point to rows in the data pages. With clustered indexes, the database manager attempts to keep the data in the data pages in the same order as the corresponding keys in the index pages. Thus the database manager attempts to insert rows with similar keys onto the same pages. If the table is reorganized, data is inserted into the data pages in the order of the index keys. The database manager does not mai

Clustered and non-clustered indexes Index architectures are classified as clustered or non-clustered. Clustered indexes are indexes whose order of the rows in the data pages corresponds to the order of the rows in the index. This order is why only one clustered index can exist in any table, whereas, many non-clustered indexes can exist in the table. In some database systems, the leaf node of the clustered index corresponds to the actual data, not a pointer to data that is found elsewhere. Both clustered and non-clustered indexes contain only keys and record identifiers in the index structure.

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