From b08d87bf34e6d65a3330b609e8115e8ab8c5e02e Mon Sep 17 00:00:00 2001
From: Yang Yang <yzhdoudou@gmail.com>
Date: Tue, 17 Sep 2019 14:53:44 -0700
Subject: [PATCH] [Intermediate Representation] Add feature column type
 interface

---
 sql/codegen/feature_column.go              | 2 ++
 sql/codegen/intermediate_representation.go | 4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/sql/codegen/feature_column.go b/sql/codegen/feature_column.go
index 40ef857ca5..dcf867bc67 100644
--- a/sql/codegen/feature_column.go
+++ b/sql/codegen/feature_column.go
@@ -20,3 +20,5 @@ package codegen
 type NumericColumn struct {
 	FieldMeta *FieldMeta
 }
+
+func (NumericColumn) isFeatureColumn() {}
diff --git a/sql/codegen/intermediate_representation.go b/sql/codegen/intermediate_representation.go
index cb19556daf..a6132fee12 100644
--- a/sql/codegen/intermediate_representation.go
+++ b/sql/codegen/intermediate_representation.go
@@ -49,7 +49,9 @@ type FieldMeta struct {
 
 // FeatureColumn indicates the feature column to be applied on the field. Please refer to
 // github.com/sql-machine-learning/sqlflow/sql/codegen/feature_column.go for detailed list of all feature columns.
-type FeatureColumn interface{}
+type FeatureColumn interface {
+	isFeatureColumn()
+}
 
 // Attribute represents an parsed entry in the WITH clause.
 type Attribute struct {