在Oracle的文档The Query Optimizer中,在
View Merging下,我找到了以下信息
The view merging optimization applies to views that contain only
selections,projections,and joins. That is,mergeable views do not contain
set operators,aggregate functions,DISTINCT,GROUP BY,CONNECT BY,and so on.
(emphasis mine)
然而,我只能猜测这样的投射实际上是指什么.
