Redundant DISTINCT on primary key column causes derived table materialization and ~2.5x slowdown

DROP DATABASE IF EXISTS perf_distinct_big;

CREATE DATABASE perf_distinct_big;

USE perf_distinct_big;

CREATE TABLE t (

  id INT PRIMARY KEY,

  pad CHAR(100)

);

CREATE TABLE d(n INT);

INSERT INTO d VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);

INSERT INTO t

SELECT a.n + 10*b.n + 100*c.n + 1000*d1.n + 10000*e.n + 100000*f.n,

       REPEAT('x', 100)

FROM d AS a

JOIN d AS b

JOIN d AS c

JOIN d AS d1

JOIN d AS e

JOIN d AS f;

EXPLAIN

SELECT COUNT(*)

FROM (

  SELECT id FROM t

) AS s;

EXPLAIN

SELECT COUNT(*)

FROM (

  SELECT DISTINCT id FROM t

) AS s;

SET profiling = 1;

SELECT SQL_NO_CACHE COUNT(*)

FROM (

  SELECT id FROM t

) AS s;

SELECT SQL_NO_CACHE COUNT(*)

FROM (

  SELECT DISTINCT id FROM t

) AS s;

SHOW PROFILES;

SELECT id:          0.18073567s

SELECT DISTINCT id: 0.44433452s