feat: add dynamic parameter expression

proto/substrait/algebra.proto

@@ -950,6 +950,7 @@ message Expression {
     Cast cast = 11;
     Subquery subquery = 12;
     Nested nested = 13;
+    DynamicParameter dynamic_parameter = 14;
 
     // deprecated: enum literals are only sensible in the context of
     // function arguments, for which FunctionArgument should now be
@@ -1604,6 +1605,16 @@ message Expression {
   }
 }
 
+// Expression that represents a dynamic parameter.
+// Dynamic parameters are identified by their 0-based index within a plan.
+message DynamicParameter {
+  // The inferred type of the dynamic parameter.
+  Type type = 1;
+
+  // The 0-based index of the dynamic parameter.
+  int32 index = 2;
+}
+
 // The description of a field to sort on (including the direction of sorting and null semantics)
 message SortField {
   Expression expr = 1;

site/docs/expressions/_config

@@ -7,3 +7,4 @@ arrange:
   - table_functions.md
   - user_defined_functions.md
   - embedded_functions.md
+  - dynamic_parameters.md

site/docs/expressions/dynamic_parameters.md

@@ -0,0 +1,12 @@
+# Dynamic Parameter Expression
+
+The dynamic parameter expression represents a placeholder within an expression whose value is determined at runtime.
+This is particularly useful for parameterized queries where certain values are not known until execution.
+Additionally, using dynamic parameters can enable other use cases, such as sharing execution plans without embedding sensitive information.
+
+A dynamic parameter expression includes the following properties:
+
+| Property | Description                                                                 | Required |
+|----------|-----------------------------------------------------------------------------|----------|
+| `type`   | Specifies the expected data type of the dynamic parameter.                  | Yes      |
+| `index`  | Indicates the 0-based position of the parameter within the plan.            | Yes      |