Abstract:Sql statement tuning is an important aspect of database performance tuning. To achieve the same effects, sql statement has a variety of wording, with different performance for the different wording. Even with only one sql statement, the oracle also has a variety of ways to implement. That is, there are multiple execution plans. The oracle compares the performance of these multiple execution plans, the cost of resources, to select the optimal execution plan. In assessing the performance of each implementation plan, the oracle needs the implementation of sql statement with the environment, that is statistical information to calculate the cost of the number of resources for each implementation plan. Therefore, it is critically important for the oracle to choose the best implementation plan to collect as much as possible accurate statistical information. Among them, the collection of the histogram plays a very important role. The experiment verifies the impact of the histogram for the sql implementation plan, which clears the circumstances under which it needs to collect histograms.