Within Mimer SQL a secondary index is implemented by creating an internal table invisible to the user. The same algorithms and structures are used for storing a secondary index as are used for an ordinary table. Concatenating the columns defined as the secondary index with the primary key of the base table forms the primary key of the index table. The secondary index tables are fully maintained internally within Mimer SQL. The algorithm used for this guarantees that the indices can never be out of step with their base table.
The SQL optimizer will automatically use secondary indices whenever there is a performance benefit. If the secondary index contains all the information required by the query the optimizer will not perform a lookup in the base table.
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