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How Does The Optimizer Choose The Query Plan/what Is Cost-based Query Optimization? |
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Answer» The optimizer generates several physical query plans that are potential execution plans. The optimizer then chooses among them by estimating the cost of each POSSIBLE physical plan based on the table and index STATISTICS available to it, and selecting the plan with the lowest ESTIMATED cost. This evaluation of the possible physical query plans is called cost-based query OPTIMIZATION. The optimizer generates several physical query plans that are potential execution plans. The optimizer then chooses among them by estimating the cost of each possible physical plan based on the table and index statistics available to it, and selecting the plan with the lowest estimated cost. This evaluation of the possible physical query plans is called cost-based query optimization. |
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