What scanning methods does the query planner perform to find data?

A query planner (for example, in a DBMS) uses several main scanning methods to find data:

1. Full Table Scan — scanning all rows of a table without using indexes. Used when indexes are absent or the selection is too large.

2. Index Scan — searching data using an index, which allows quickly finding the needed records without scanning the entire table.

3. Range Scan — reading a sequential range of values from an index, effective for queries with conditions like BETWEEN or >, <.

4. Unique Index Scan — fast search for a single record by a unique key.

5. Hash Scan — used in some DBMSs for quick search using hash tables.

The choice of method depends on the query structure, the presence of indexes, and data statistics.