fix: left join returns wrong answer

Author: xudong963

src/query/service/src/sql/planner/binder/join.rs

@@ -448,9 +448,11 @@ impl<'a> JoinConditionResolver<'a> {
         // Bump types of left conditions and right conditions
         let left_type = left.data_type();
         let right_type = right.data_type();
-        let least_super_type = compare_coercion(&left_type, &right_type)?;
-        left = wrap_cast_if_needed(left, &least_super_type);
-        right = wrap_cast_if_needed(right, &least_super_type);
+        if left_type.ne(&right_type) {
+            let least_super_type = compare_coercion(&left_type, &right_type)?;
+            left = wrap_cast_if_needed(left, &least_super_type);
+            right = wrap_cast_if_needed(right, &least_super_type);
+        }
 
         if left_used_columns.is_subset(&left_columns)
             && right_used_columns.is_subset(&right_columns)

src/query/service/src/sql/planner/binder/scalar_common.rs

@@ -86,16 +86,12 @@ pub fn split_equivalent_predicate(scalar: &Scalar) -> Option<(Scalar, Scalar)> {
 }
 
 pub fn wrap_cast_if_needed(scalar: Scalar, target_type: &DataTypeImpl) -> Scalar {
-    if scalar.data_type() != *target_type {
-        let cast = CastExpr {
-            from_type: Box::new(scalar.data_type()),
-            argument: Box::new(scalar),
-            target_type: Box::new(target_type.clone()),
-        };
-        cast.into()
-    } else {
-        scalar
+    CastExpr {
+        from_type: Box::new(scalar.data_type()),
+        argument: Box::new(scalar),
+        target_type: Box::new(target_type.clone()),
     }
+    .into()
 }
 
 pub fn satisfied_by(scalar: &Scalar, prop: &RelationalProperty) -> bool {

tests/logictest/suites/crdb/join

@@ -661,6 +661,15 @@ B NULL B
 C NULL C
 E NULL E
 
+statement query ITIT
+SELECT * FROM str1 LEFT OUTER JOIN str2 ON str1.s = str2.s order by str1.a;
+
+----
+1 a NULL NULL
+2 A 1 A
+3 c NULL NULL
+4 D NULL NULL
+
 -- statement query
 -- SELECT s, str1.s, str2.s FROM str1 FULL OUTER JOIN str2 USING(s);