diff --git a/executor/aggregate_test.go b/executor/aggregate_test.go
index 5bd7fe00ae207..d2a64108354fb 100644
--- a/executor/aggregate_test.go
+++ b/executor/aggregate_test.go
@@ -580,6 +580,16 @@ func (s *testSuite1) TestIssue13652(c *C) {
 	c.Assert(err.Error(), Equals, "[planner:1055]Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'test.t.a' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by")
 }
 
+func (s *testSuite1) TestIssue14947(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("set sql_mode = 'ONLY_FULL_GROUP_BY'")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int)")
+	tk.MustQuery("select ((+a+1)) as tmp from t group by tmp")
+	tk.MustQuery("select count(*), (case when a=1 then 0 else 2 end) as xx from t group by xx;")
+}
+
 func (s *testSuite1) TestHaving(c *C) {
 	tk := testkit.NewTestKitWithInit(c, s.store)
 
diff --git a/planner/core/logical_plan_builder.go b/planner/core/logical_plan_builder.go
index cab17c946c623..83cfdb8070325 100644
--- a/planner/core/logical_plan_builder.go
+++ b/planner/core/logical_plan_builder.go
@@ -1754,7 +1754,7 @@ func (b *PlanBuilder) checkOnlyFullGroupByWithGroupClause(p LogicalPlan, sel *as
 		if field.Auxiliary {
 			continue
 		}
-		checkExprInGroupBy(p, field.Expr, offset, ErrExprInSelect, gbyCols, gbyExprs, notInGbyCols)
+		checkExprInGroupBy(p, getInnerFromParenthesesAndUnaryPlus(field.Expr), offset, ErrExprInSelect, gbyCols, gbyExprs, notInGbyCols)
 	}
 
 	if sel.OrderBy != nil {