Home » Oracle » 1z0-117 » What would you do to influence the optimizer for better selectivity?
Examine the Exhibit to view the structure of an indexes for the SALES table.
The SALES table has 4594215 rows. The CUST_ID column has 2079 distinct values.
What would you do to influence the optimizer for better selectivity?
Exhibit:
A. Drop bitmap index and create balanced B*Tree index on the CUST_ID column.
B. Create a height-balanced histogram for the CUST_ID column.
C. Gather statistics for the indexes on the SALES table.
D. Use the ALL_ROWS hint in the query.
Correct Answer: D
Explanation/Reference:
OPTIMIZER_MODE establishes the default behavior for choosing an optimization approach for the instance. Values: FIRST_ROWS_N - The optimizer uses a cost-based approach and optimizes with a goal of best response time to return the first n rows (where n = 1, 10, 100, 1000). FIRST_ROWS - The optimizer uses a mix of costs and heuristics to find a best plan for fast delivery of the first few rows. ALL_ROWS - The optimizer uses a cost-based approach for all SQL statements in the session and optimizes with a goal of best throughput (minimum resource use to complete the entire statement).
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