To recap, Attributes form the properties of a derived table.
Each LogicalPlan has Attributes as output since each one can be part of
a query and as such its result are sent to its consumer.
This change essentially removes the name id comparison so any changes
applied to existing expressions should work as long as the said
expressions are semantically equivalent.
This change enforces the hashCode and equals which has the side-effect
of using hashCode as identifiers for each expression.
By removing any property from an Attribute, the various components need
to look the original source for comparison which, while annoying, should
prevent a reference from getting out of sync with its source due to
optimizations.
Essentially going forward there are only 3 types of NamedExpressions:
Alias - user define (implicit or explicit) name
FieldAttribute - field backed by Elasticsearch
ReferenceAttribute - a reference to another source acting as an
Attribute. Typically the Attribute of an Alias.
* Remove the usage of NamedExpression as basis for all Expressions.
Instead, restrict their use only for named context, such as projections
by using Aliasing instead.
* Remove different types of Attributes and allow only FieldAttribute,
UnresolvedAttribute and ReferenceAttribute. To avoid issues with
rewrites, resolve the references inside the QueryContainer so the
information always stays on the source.
* Side-effect, simplify the rules as the state for InnerAggs doesn't
have to be contained anymore.
* Improve ResolveMissingRef rule to handle references to named
non-singular expression tree against the same expression used up the
tree.
#49693 backport to 7.x
(cherry picked from commit 5d095e2173bcbf120f534a6f2a584185a7879b57)
5b896c5bb5