- All Implemented Interfaces:
- java.util.Comparator<SubstituteExpressionVisitor>
- Enclosing class:
- GroupByNode
private static class GroupByNode.ExpressionSorter
extends java.lang.Object
implements java.util.Comparator<SubstituteExpressionVisitor>
Comparator class for GROUP BY expression substitution.
This class enables the sorting of a collection of
SubstituteExpressionVisitor instances. We sort the visitors
during the tree manipulation processing in order to process
expressions of higher complexity prior to expressions of
lower complexity. Processing the expressions in this order ensures
that we choose the best match for an expression, and thus avoids
problems where we substitute a sub-expression instead of the
full expression. For example, if the statement is:
... GROUP BY a+b, a, a*(a+b), a+b+c
we'll process those expressions in the order: a*(a+b),
a+b+c, a+b, then a.