Critical Description
When inferring constraints from children, Join's condition can be simplified as None.
For example,
val testRelation = LocalRelation('a.int)
val x = testRelation.as("x")
val y = testRelation.where($"a" === 2 && !($"a" === 2)).as("y")
x.join
.where($"x.a" === $"y.a")
The plan will become
Join Inner
:- LocalRelation <empty>, a#23
+- LocalRelation <empty>, a#224
And the Cartesian products check will throw exception.
Propagate empty relation before checking Cartesian products, and the issue is resolved.
