diff --git a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/FlintSparkIndexBuilder.scala b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/FlintSparkIndexBuilder.scala
index 7171bf1af..95e351f7d 100644
--- a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/FlintSparkIndexBuilder.scala
+++ b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/FlintSparkIndexBuilder.scala
@@ -34,6 +34,14 @@ abstract class FlintSparkIndexBuilder(flint: FlintSpark) {
       .toMap
   }
 
+  /**
+   * Add index options.
+   *
+   * @param options
+   *   index options
+   * @return
+   *   builder
+   */
   def options(options: FlintSparkIndexOptions): this.type = {
     this.indexOptions = options
     this
diff --git a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/skipping/FlintSparkSkippingIndex.scala b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/skipping/FlintSparkSkippingIndex.scala
index c871a1900..2eebffebf 100644
--- a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/skipping/FlintSparkSkippingIndex.scala
+++ b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/skipping/FlintSparkSkippingIndex.scala
@@ -33,9 +33,9 @@ import org.apache.spark.sql.types.StructType
  * @param indexedColumns
  *   indexed column list
  */
-case class FlintSparkSkippingIndex(
+class FlintSparkSkippingIndex(
     tableName: String,
-    indexedColumns: Seq[FlintSparkSkippingStrategy],
+    val indexedColumns: Seq[FlintSparkSkippingStrategy],
     override val options: FlintSparkIndexOptions = empty)
     extends FlintSparkIndex {
 
diff --git a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlAstBuilder.scala b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlAstBuilder.scala
index 3a67625de..9f3539b09 100644
--- a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlAstBuilder.scala
+++ b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlAstBuilder.scala
@@ -5,11 +5,13 @@
 
 package org.opensearch.flint.spark.sql
 
-import org.antlr.v4.runtime.tree.RuleNode
+import org.antlr.v4.runtime.tree.{ParseTree, RuleNode}
 import org.opensearch.flint.spark.FlintSpark
 import org.opensearch.flint.spark.sql.covering.FlintSparkCoveringIndexAstBuilder
 import org.opensearch.flint.spark.sql.skipping.FlintSparkSkippingIndexAstBuilder
 
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+
 /**
  * Flint Spark AST builder that builds Spark command for Flint index statement. This class mix-in
  * all other AST builders and provides util methods.
@@ -20,6 +22,10 @@ class FlintSparkSqlAstBuilder
     with FlintSparkCoveringIndexAstBuilder
     with SparkSqlAstBuilder {
 
+  override def visit(tree: ParseTree): LogicalPlan = {
+    tree.accept(this).asInstanceOf[LogicalPlan]
+  }
+
   override def aggregateResult(aggregate: AnyRef, nextResult: AnyRef): AnyRef =
     if (nextResult != null) nextResult else aggregate
 }
diff --git a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlParser.scala b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlParser.scala
index 4bc828644..0fa146b9d 100644
--- a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlParser.scala
+++ b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/FlintSparkSqlParser.scala
@@ -54,7 +54,7 @@ class FlintSparkSqlParser(sparkParser: ParserInterface) extends ParserInterface
 
   override def parsePlan(sqlText: String): LogicalPlan = parse(sqlText) { flintParser =>
     try {
-      flintAstBuilder.visit(flintParser.singleStatement()).asInstanceOf[LogicalPlan]
+      flintAstBuilder.visit(flintParser.singleStatement())
     } catch {
       // Fall back to Spark parse plan logic if flint cannot parse
       case _: ParseException => sparkParser.parsePlan(sqlText)
diff --git a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/SparkSqlAstBuilder.scala b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/SparkSqlAstBuilder.scala
index 8a5855d47..d4e4db104 100644
--- a/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/SparkSqlAstBuilder.scala
+++ b/flint-spark-integration/src/main/scala/org/opensearch/flint/spark/sql/SparkSqlAstBuilder.scala
@@ -15,7 +15,8 @@ import org.opensearch.flint.spark.sql.FlintSparkSqlExtensionsParser.{PropertyKey
 import org.apache.spark.sql.catalyst.parser.ParserUtils.string
 
 /**
- * AST builder that builds for common rule in Spark SQL grammar.
+ * AST builder that builds for common rule in Spark SQL grammar. The main logic is modified slightly
+ * from Spark AstBuilder code.
  */
 trait SparkSqlAstBuilder extends FlintSparkSqlExtensionsVisitor[AnyRef] {