Return error on LABEL with string type (#1000)

* Return error on LABEL with string type

* fix CI

Author: tonyyang-svail

pkg/sql/codegen.go

@@ -228,7 +228,7 @@ func newFiller(pr *extendedSelect, ds *trainAndValDataset, fts fieldTypes, db *D
 		} else if v == "BIGINT" {
 			labelDtype = "int64"
 		} else {
-			log.Fatalf("Unsupported label data type: %s", v)
+			return nil, fmt.Errorf("unsupported label data type: %s", v)
 		}
 	}
 	r.Y = &FeatureMeta{

pkg/sql/codegen_test.go

@@ -15,6 +15,7 @@ package sql
 
 import (
 	"io/ioutil"
+	"strings"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -85,3 +86,22 @@ func TestCodeGenPredict(t *testing.T) {
 
 	a.NoError(genTF(ioutil.Discard, r, nil, fts, testDB))
 }
+
+func TestLabelAsStringType(t *testing.T) {
+	a := assert.New(t)
+	r, e := newParser().Parse(`SELECT customerID, gender FROM churn.train
+TRAIN DNNClassifier
+WITH
+	model.n_classes = 3,
+	model.hidden_units = [10, 20]
+COLUMN customerID
+LABEL gender
+INTO sqlflow_models.my_dnn_model;`)
+	a.NoError(e)
+
+	fts, e := verify(r, testDB)
+	a.NoError(e)
+	e = genTF(ioutil.Discard, r, nil, fts, testDB)
+	a.NotNil(e)
+	a.True(strings.HasPrefix(e.Error(), "unsupported label data type:"))
+}