DOCS-14252 create match expressions for aggregation

source/includes/expr-operators-and-indexes.rst

@@ -0,0 +1,13 @@
+Starting in MongoDB 5.0, the :expression:`$eq`, :expression:`$lt`,
+:expression:`$lte`, :expression:`$gt`, and :expression:`$gte` comparison
+operators placed in an :query:`$expr` operator can use an index on the
+``from`` collection referenced in a :pipeline:`$lookup` stage.
+Limitations:
+
+- :ref:`Multikey indexes <index-type-multikey>` are not used.
+
+- Indexes are not used for comparisons where the operand is an array or
+  the operand type is undefined.
+
+- Indexes are not used for comparisons with more than one :ref:`field
+  path <agg-quick-ref-field-paths>` operand.

source/includes/fact-let-variable-access-note.rst

@@ -1,21 +1,18 @@
 .. note::
 
    To reference variables in :ref:`pipeline <lookup-join-pipeline>`
-   stages, use the ``"$$<variable>"`` syntax. 
+   stages, use the ``"$$<variable>"`` syntax.
 
    The :ref:`let <lookup-join-let>` variables can be accessed by the
    stages in the :ref:`pipeline <lookup-join-pipeline>`, including
    additional :pipeline:`$lookup` stages nested in the ``pipeline``.
 
    - A :pipeline:`$match` stage requires the use of an
-     :query:`$expr` operator to access the variables.
-     :query:`$expr` allows the use of aggregation expressions
-     inside of the :pipeline:`$match` syntax.
+     :query:`$expr` operator to access the variables. The :query:`$expr`
+     operator allows the use of aggregation expressions inside of the
+     :pipeline:`$match` syntax.
 
-     The :query:`$expr` operator only uses indexes on the joined
-     ``from`` collection for equality matches. Non-equality match
-     queries, such as range queries, cannot use indexes on the joined
-     ``from`` collection.
+     .. include:: /includes/expr-operators-and-indexes.rst
 
    - Other (non-:pipeline:`$match`) stages in the :ref:`pipeline
      <lookup-join-pipeline>` do not

source/reference/operator/aggregation/lookup.txt

@@ -15,7 +15,7 @@ Definition
 
 .. pipeline:: $lookup
 
-   .. versionadded:: 3.2
+   .. versionchanged:: 5.0
 
    Performs a left outer join to an unsharded collection in the *same*
    database to filter in documents from the "joined" collection for
@@ -772,16 +772,16 @@ The operation corresponds to this pseudo-SQL statement:
       AND instock >= orders.ordered
    );
 
-The :query:`$expr` operator only uses indexes on the ``from``
-collection for equality matches. For example, if the index
-``{ stock_item: 1, instock: 1 }`` exists on the ``warehouses``
-collection:
+.. include:: /includes/expr-operators-and-indexes.rst
+
+For example, if the index ``{ stock_item: 1, instock: 1 }`` exists on
+the ``warehouses`` collection:
 
 - The equality match on the ``warehouses.stock_item`` field uses the
   index.
 
 - The range part of the query on the ``warehouses.instock`` field
-  does not use the indexed field in the compound index.
+  also uses the indexed field in the compound index.
 
 .. seealso:: 
 

source/reference/operator/query/expr.txt

@@ -13,7 +13,7 @@ $expr
 Definition
 ----------
 
-.. versionadded:: 3.6
+.. versionchanged:: 5.0
 
 .. query:: $expr
 
@@ -33,18 +33,14 @@ Definition
 Behavior
 --------
 
-- :query:`$expr` can build query expressions that compare fields 
-  from the same document in a :pipeline:`$match` stage.
+:query:`$expr` can build query expressions that compare fields from the
+same document in a :pipeline:`$match` stage.
 
-  - If the :pipeline:`$match` stage is part of a :pipeline:`$lookup`
-    stage, :query:`$expr` can compare fields using ``let`` variables.
-    See :ref:`lookup-multiple-joins` for an example. 
+If the :pipeline:`$match` stage is part of a :pipeline:`$lookup` stage,
+:query:`$expr` can compare fields using ``let`` variables. See
+:ref:`lookup-multiple-joins` for an example. 
 
-  - :query:`$expr` only uses indexes on the ``from`` collection for
-    equality matches in a :pipeline:`$match` stage.
-
-- :query:`$expr` does not support
-  :ref:`multikey indexes <index-type-multikey>`.
+.. include:: /includes/expr-operators-and-indexes.rst
 
 Examples
 --------

source/release-notes/5.0.txt

@@ -47,6 +47,13 @@ Starting in MongoDB 5.0, you can specify multiple input expressions for
 the :expression:`$ifNull` expression before returning a replacement
 expression.
 
+Comparison Operators and Indexes with ``$expr`` Operator
+````````````````````````````````````````````````````````
+
+Starting in MongoDB 5.0, the :expression:`$eq`, :expression:`$lt`,
+:expression:`$lte`, :expression:`$gt`, and :expression:`$gte` operators
+placed in an :query:`$expr` operator can use an index.
+
 Aggregate ``let`` Option
 ````````````````````````