Modify the overriden toSql

Author: ljfgem

coral-hive/src/main/java/com/linkedin/coral/transformers/CoralRelToSqlNodeConverter.java

@@ -350,15 +350,14 @@ private SqlNode generateRightChildForSqlJoinWithLateralViews(BiRel e, Result rig
   }
 
   /**
-   * Override this method to handle the conversion for RelNode `f(x).y.z` where `f` is an UDF, which
+   * Override this method to handle the conversion for RelNode `f(x).y.z` where `f` is an operator, which
    * returns a struct containing field `y`, `y` is also a struct containing field `z`.
    *
    * Calcite will convert this RelNode to a SqlIdentifier directly (check
    * {@link org.apache.calcite.rel.rel2sql.SqlImplementor.Context#toSql(RexProgram, RexNode)}),
    * which is not aligned with our expectation since we want to apply transformations on `f(x)` with
    * {@link com.linkedin.coral.common.transformers.SqlCallTransformer}. Therefore, we override this
    * method to convert `f(x)` to SqlCall, `.` to {@link com.linkedin.coral.common.functions.FunctionFieldReferenceOperator#DOT}
-   * and `y.z` to SqlIdentifier.
    */
   @Override
   public Context aliasContext(Map<String, RelDataType> aliases, boolean qualified) {
@@ -374,11 +373,14 @@ public SqlNode toSql(RexProgram program, RexNode rex) {
             accessNames.add(((RexFieldAccess) referencedExpr).getField().getName());
             referencedExpr = ((RexFieldAccess) referencedExpr).getReferenceExpr();
           }
-          if (referencedExpr.getKind() == SqlKind.OTHER_FUNCTION) {
+          if (referencedExpr.getKind() == SqlKind.OTHER_FUNCTION || referencedExpr.getKind() == SqlKind.CAST) {
             SqlNode functionCall = toSql(program, referencedExpr);
             Collections.reverse(accessNames);
-            return FunctionFieldReferenceOperator.DOT.createCall(SqlParserPos.ZERO, functionCall,
-                new SqlIdentifier(String.join(".", accessNames), POS));
+            for (String accessName : accessNames) {
+              functionCall = FunctionFieldReferenceOperator.DOT.createCall(SqlParserPos.ZERO, functionCall,
+                  new SqlIdentifier(accessName, POS));
+            }
+            return functionCall;
           }
         }
         return super.toSql(program, rex);