planner: make var_samp can be used as a window function (pingcap#53130)

close pingcap#52933

Author: 0xPoe

pkg/executor/window_test.go

@@ -470,3 +470,12 @@ func TestIssue45964And46050(t *testing.T) {
 	testReturnColumnNullableAttribute(tk, "cume_dist()", false)
 	testReturnColumnNullableAttribute(tk, "percent_rank()", false)
 }
+
+func TestVarSampAsAWindowFunction(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t1 (c1 int)")
+	tk.MustExec("select var_samp(c1) from t1")
+	tk.MustExec("select c1, var_samp(c1) over (partition by c1) from t1")
+}

pkg/parser/parser.go

@@ -8418,7 +8418,11 @@ SumExpr:
 	}
 |	builtinVarSamp '(' BuggyDefaultFalseDistinctOpt Expression ')' OptWindowingClause
 	{
-		$$ = &ast.AggregateFuncExpr{F: $1, Args: []ast.ExprNode{$4}, Distinct: $3.(bool)}
+		if $6 != nil {
+			$$ = &ast.WindowFuncExpr{Name: $1, Args: []ast.ExprNode{$4}, Distinct: $3.(bool), Spec: *($6.(*ast.WindowSpec))}
+		} else {
+			$$ = &ast.AggregateFuncExpr{F: $1, Args: []ast.ExprNode{$4}, Distinct: $3.(bool)}
+		}
 	}
 |	"JSON_ARRAYAGG" '(' Expression ')' OptWindowingClause
 	{