Can indexes in a database sometimes negatively impact performance, and in what cases does this happen?

Indexes in a database do not always improve performance, and in some cases, they can even degrade it. This happens, for example, when:

• Indexes are created on columns with low selectivity (many repeating values), then the DBMS may prefer a full table scan.
• The table is very small, and the cost of using the index exceeds the benefit.
• Indexes are created on frequently updated columns — then insert, update, and delete operations slow down because of the need to maintain the index.
• Complex queries are used where the index does not cover all conditions, requiring additional operations.

Therefore, it is important to analyze which indexes are truly needed and to conduct performance testing.