Comment rationale for not directly comparing Dictionary types

apache · Jan 19, 2022 · e27110f · e27110f
1 parent c4db8f3
commit e27110f
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Showing 2 changed files with 9 additions and 1 deletion.
diff --git a/datafusion/src/physical_plan/coercion_rule/binary_rule.rs b/datafusion/src/physical_plan/coercion_rule/binary_rule.rs
@@ -77,6 +77,8 @@ pub(crate) fn coerce_types(
 }
 
 fn comparison_eq_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
+    // can't compare dictionaries directly due to
+    // https://github.com/apache/arrow-rs/issues/1201
     if lhs_type == rhs_type && !is_dictionary(lhs_type) {
         // same type => equality is possible
         return Some(lhs_type.clone());
@@ -90,6 +92,8 @@ fn comparison_order_coercion(
     lhs_type: &DataType,
     rhs_type: &DataType,
 ) -> Option<DataType> {
+    // can't compare dictionaries directly due to
+    // https://github.com/apache/arrow-rs/issues/1201
     if lhs_type == rhs_type && !is_dictionary(lhs_type) {
         // same type => all good
         return Some(lhs_type.clone());

diff --git a/datafusion/src/physical_plan/expressions/coercion.rs b/datafusion/src/physical_plan/expressions/coercion.rs
@@ -162,8 +162,10 @@ pub fn numerical_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<Da
         return None;
     };
 
-    // same type => all good
+    // can't compare dictionaries directly due to
+    // https://github.com/apache/arrow-rs/issues/1201
     if lhs_type == rhs_type && !is_dictionary(lhs_type) {
+        // same type => all good
         return Some(lhs_type.clone());
     }
 
@@ -186,6 +188,8 @@ pub fn numerical_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<Da
 
 // coercion rules for equality operations. This is a superset of all numerical coercion rules.
 pub fn eq_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
+    // can't compare dictionaries directly due to
+    // https://github.com/apache/arrow-rs/issues/1201
     if lhs_type == rhs_type && !is_dictionary(lhs_type) {
         // same type => equality is possible
         return Some(lhs_type.clone());