dba_histograms等高直方圖和等頻直方圖的理解

1>等高直方圖: Distinct column values for  one table column >254

   endpoint number 對應 bucket number,endpoint value對應column值的範圍:

Endpoint number   endpoint value

1.                                                 8

2.                                                         10

3.                                                         50

4.                                                         90

5.                                                        100

說明:對於等高直方圖,bucket 1對應的column值為 column value<=8 and<10

Bucket 5對應的值為100

 

1>等頻直方圖: Distinct column values for  one table column <254

  endpoint number 對應值為 累積的column value 個數(計算重複的column value),endpoint value對應 實際 column值