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Indexes are the primary mechanism for speeding up query performance in Oracle Database. Like an index in a book, a database index allows Oracle to find rows quickly without scanning every row in a table. This lesson covers index types, the Oracle optimiser, and essential performance tuning techniques.
An index is a database object that stores a sorted copy of selected column values along with pointers (ROWIDs) to the corresponding table rows.
Without an index: Oracle performs a full table scan — reads every row. With an index: Oracle performs an index lookup — jumps directly to matching rows.
The most common index type — a balanced tree structure:
CREATE INDEX emp_lastname_idx ON employees(last_name);
=) and range (<, >, BETWEEN) queriesAn index on multiple columns:
CREATE INDEX emp_dept_sal_idx ON employees(department_id, salary);
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