On Oracle Histograms
Yang Ying · Journal of Chongqing Institute of Technology · 2008
Histograms may help the Oracle optimizer in deciding whether to use an index vs.a full-table scan(where index values are skewed) or help the optimizer determine the fastest table-join order.If there is a column in your database that has a peculiar data distribution and is used in a where clause,then you may need to create a histogram on that column.This paper mainly discusses two types of histograms,Frequency histograms and Height Balanced histograms,including their principles and strategies,and their advantages and disadvantages are also discussed.