added select plan by id

store/postgres.go

@@ -44,3 +44,12 @@ func (store *postgresStore) SelectPlans() ([]*models.Plan, error) {
 	}
 	return plans, nil
 }
+
+func (store *postgresStore) SelectPlanByID(id int) (*models.Plan, error) {
+	plan := models.Plan{}
+	err := store.db.Get(&plan, store.db.Rebind("SELECT plan_id, plan_date FROM plans WHERE plan_id = ?"), id)
+	if err != nil {
+		return nil, err
+	}
+	return &plan, nil
+}