Can an index slow down reading (SELECT)?

Yes, an index can slow down reading (SELECT) in some cases:

• If the query selects a large portion of the table, using an index may lead to additional read operations (index + data), which is slower than a full table scan.
• For complex queries with many joins and conditions, the optimizer may choose an inefficient plan using an index.
• If the index is fragmented or contains many levels, traversing the index can be costly.
• When using an inappropriate index type for a specific query (e.g., bitmap index for OLTP queries).

Therefore, it is important to analyze query execution plans and choose indexes that truly speed up reading rather than degrade performance.