experimental: add a converter for logical plan to sql (#18)

* (experimental): add a converter for logical plan to sql

* format code

* feat(logical): add relationship variables in logical plan

* format code

* fix warnings

* format code

* fix warning

Author: ChunxuTang

rust/lance-graph/src/datafusion_planner.rs

@@ -468,6 +468,7 @@ mod tests {
             target_variable: "b".to_string(),
             relationship_types: vec!["KNOWS".to_string()],
             direction: crate::ast::RelationshipDirection::Outgoing,
+            relationship_variable: None,
             properties: Default::default(),
         };
         let project = LogicalOperator::Project {

rust/lance-graph/src/lib.rs

@@ -46,6 +46,7 @@ pub mod query;
 pub mod query_processor;
 pub mod semantic;
 pub mod source_catalog;
+pub mod sql_converter;
 
 /// Maximum allowed hops for variable-length relationship expansion (e.g., *1..N)
 pub const MAX_VARIABLE_LENGTH_HOPS: u32 = 20;

rust/lance-graph/src/logical_plan.rs

@@ -36,6 +36,7 @@ pub enum LogicalOperator {
         target_variable: String,
         relationship_types: Vec<String>,
         direction: RelationshipDirection,
+        relationship_variable: Option<String>,
         properties: HashMap<String, PropertyValue>,
     },
 
@@ -46,6 +47,7 @@ pub enum LogicalOperator {
         target_variable: String,
         relationship_types: Vec<String>,
         direction: RelationshipDirection,
+        relationship_variable: Option<String>,
         min_length: Option<u32>,
         max_length: Option<u32>,
     },
@@ -308,6 +310,7 @@ impl LogicalPlanner {
                         target_variable: target_variable.clone(),
                         relationship_types: segment.relationship.types.clone(),
                         direction: segment.relationship.direction.clone(),
+                        relationship_variable: segment.relationship.variable.clone(),
                         properties: segment.relationship.properties.clone(),
                     }
                 }
@@ -317,6 +320,7 @@ impl LogicalPlanner {
                     target_variable: target_variable.clone(),
                     relationship_types: segment.relationship.types.clone(),
                     direction: segment.relationship.direction.clone(),
+                    relationship_variable: segment.relationship.variable.clone(),
                     min_length: length_range.min,
                     max_length: length_range.max,
                 },
@@ -326,6 +330,7 @@ impl LogicalPlanner {
                     target_variable: target_variable.clone(),
                     relationship_types: segment.relationship.types.clone(),
                     direction: segment.relationship.direction.clone(),
+                    relationship_variable: segment.relationship.variable.clone(),
                     properties: segment.relationship.properties.clone(),
                 },
             };