How does the state of an index change after delete and re-insert operations in an SQL table?

After deleting records from a SQL table, the index state changes as follows:

• Deleted records are removed from the index, meaning the corresponding keys and row references are deleted.
• However, the physical freeing of space within the index structure may not happen immediately, depending on the DBMS and index type.

When inserting records again:

• If new records with the same key values are inserted, they are added to the index as new entries.
• In some DBMSs (e.g., with auto-increment keys), new records may receive new key values, which affects the index.

As a result, the index reflects the current state of the table — it contains only existing records. During intensive delete and insert operations, periodic reorganization or rebuilding of the index may be necessary to optimize performance.

Example: if the table has an index on the "id" column, and you delete a record with id=5, the index will no longer contain this record. When a new record with id=5 is inserted (if allowed), the index will be updated to include the new record.