What are the advantages and disadvantages of using low-selectivity indexes in a database?

Advantages of low-selectivity indexes:

• They can speed up query execution if filtering by this column still reduces the number of rows processed.
• Useful as part of composite indexes where the low-selectivity index column is placed first.

Disadvantages:

• Low-selectivity indexes occupy space and require resources for updates when data changes.
• They may not be used by the query optimizer if the selectivity is too low, leading to additional overhead.
• Frequent data updates can reduce write performance.

Overall, low-selectivity indexes should be used cautiously and only if they genuinely improve the performance of specific queries.