From the instance valuedistributionof attributes shown in Listing 5, GASF determines that it has to create another questionnaire to further drill down for the searched object.
根据清单5中所示的属性的实例值分布,GASF判断必须创建另一调查表,以进一步挖掘搜索对象。
3
Without column data-valuedistribution information in the catalog, DB2 will assume an even distribution of values, which may lead the optimizer to a sub-optimal access path.