Expand Unary Logical Operator

Expand is a unary logical operator that represents Cube, Rollup, GroupingSets and TimeWindow logical operators after they have been resolved at analysis phase.

FIXME Examples for
1. Cube
2. Rollup
3. GroupingSets
4. See TimeWindow

val q = ...

scala> println(q.queryExecution.logical.numberedTreeString)
...

Note	`Expand` logical operator is resolved to ExpandExec physical operator in BasicOperators execution planning strategy.

Table 1. Expand’s Properties
Name	Description
`references`	`AttributeSet` from projections
`validConstraints`	Empty set of expressions

Expand logical operator is resolved to at analysis phase in the following logical evaluation rules:

Note	Aggregate → (Cube\|Rollup\|GroupingSets) → constructAggregate → constructExpand

val spark: SparkSession = ...
// using q from the example above
val plan = q.queryExecution.logical

scala> println(plan.numberedTreeString)
...FIXME

Expand takes the following when created:

Expand