Window Unary Logical Operator
Window is a unary logical operator that is created for:
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a collection of named expressions (for windows)
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a collection of expressions (for partitions)
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a collection of
SortOrder(for sorting) and a child logical plan.
The output (collection of Attributes) is the child’s attributes and the window’s.
Window logical plan is a subject of pruning unnecessary window expressions in ColumnPruning rule and pushing filter operators in PushDownPredicate rule.