DROP TABLE IF EXISTS diaries;
SET NAMES utf8mb4;
CREATE TABLE diaries (
created_at datetime,
title varchar(256),
KEY created_at_key(created_at)
) DEFAULT CHARSET=utf8mb4;
INSERT INTO diaries VALUES ("1000-01-01 00:00:00", "The start");
INSERT INTO diaries VALUES ("2012-10-25 16:18:29", "Today is shiny day.");
INSERT INTO diaries VALUES ("9999-12-31 23:59:59", "The end");
SELECT *
FROM diaries FORCE INDEX(created_at_key)
WHERE created_at = "2012-10-25 16:18:29";
created_at	title
2012-10-25 16:18:29	Today is shiny day.
DROP TABLE diaries;
