Before SQL is executed, the DB2 optimizer estimates the cost of the candidate access paths and selects the path with the least estimated cost.

在执行SQL之前，DB 2优化器会评估候选访问路径的成本，然后选择成本最低的路径。

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So the most optimal path planning is regard as the problem of searching for roads which have the least cost in a road net.

所以，最优路径规划最终都可以归结为在特定的道路网络中搜索总代价最小的目标路径问题。

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The first one is community model based on shortest path, the second one is based on least cost by introducing a turn penalty, the last one is community model based on probability and turn penalty.

第一种是社区最短路径模型，第二种是社区最小代价模型，第三种是引入概率的最小代价模型。

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