Fix couler evaluate step (#2848)

* fix couler generate evaluation step

* fix couler evaluate step

* fix test

Author: typhoonzero

go/cmd/sqlflowserver/e2e_workflow_test.go

@@ -120,25 +120,30 @@ func CaseWorkflowTrainAndPredictDNN(t *testing.T) {
 	sqlProgram := fmt.Sprintf(`
 SELECT * FROM %s LIMIT 10;
 
-SELECT *
-FROM %s
+SELECT * FROM %s
 TO TRAIN DNNClassifier
 WITH
 	model.n_classes = 3,
 	model.hidden_units = [10, 20],
 	validation.select = "SELECT * FROM %s"
-COLUMN sepal_length, sepal_width, petal_length, petal_width
 LABEL class
 INTO %s;
 
-SELECT *
-FROM %s
+SELECT * FROM %s
+TO EVALUATE %s
+WITH validation.metrics="Accuracy"
+LABEL class
+INTO %s.sqlflow_iris_eval_result;
+
+SELECT * FROM %s
 TO PREDICT %s.class
 USING %s;
 
 SELECT *
 FROM %s LIMIT 5;
-	`, caseTrainTable, caseTrainTable, caseTestTable, caseInto, caseTestTable, casePredictTable, caseInto, casePredictTable)
+	`, caseTrainTable, caseTrainTable, caseTestTable, caseInto,
+		caseTestTable, caseInto, caseDB,
+		caseTestTable, casePredictTable, caseInto, casePredictTable)
 
 	conn, err := createRPCConn()
 	if err != nil {

go/workflow/couler/codegen.go

@@ -137,7 +137,7 @@ func GenFiller(programIR []ir.SQLFlowStmt, session *pb.Session) (*Filler, error)
 
 	for _, sqlIR := range programIR {
 		switch i := sqlIR.(type) {
-		case *ir.NormalStmt, *ir.PredictStmt, *ir.ExplainStmt:
+		case *ir.NormalStmt, *ir.PredictStmt, *ir.ExplainStmt, *ir.EvaluateStmt:
 			// TODO(typhoonzero): get model image used when training.
 			sqlStmt := &sqlStatement{
 				OriginalSQL: sqlIR.GetOriginalSQL(), IsExtendedSQL: sqlIR.IsExtended(),