Get the latest data - optimize the SQL query

Question

I am using the following SQL query in order to get the latest data from the database.

SELECT d.id AS id_d,
       d.id_user AS id_du,
       d.id_channel AS id_dc,
       d.datetime_logged AS logged

FROM discord AS d
JOIN discord_users AS du
ON d.id_user = du.id
WHERE datetime_logged IN (SELECT MAX(datetime_logged) FROM discord)
ORDER BY du.data_name ASC

And here's how the database looks like:

CREATE TABLE IF NOT EXISTS `discord` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `id_user` int(11) NOT NULL,
  `id_channel` varchar(50) NOT NULL,
  `id_game` int(11) NOT NULL,
  `data_muted_server` tinyint(4) NOT NULL,
  `data_muted_self` tinyint(4) NOT NULL,
  `data_deafen_server` tinyint(4) NOT NULL,
  `data_deafen_self` tinyint(4) NOT NULL,
  `data_suppressed` tinyint(4) NOT NULL,
  `data_status` varchar(10) NOT NULL,
  `data_game` text,
  `datetime_logged` datetime NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id` (`id`)
)

CREATE TABLE IF NOT EXISTS `discord_users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `data_id` text NOT NULL,
  `data_name` varchar(50) NOT NULL,
  `data_avatar` text,
  PRIMARY KEY (`id`),
  UNIQUE KEY `id` (`id`)
)

That query takes "ages" to load. But if I remove WHERE datetime_logged IN (SELECT MAX(datetime_logged) FROM discord) and add LIMIT 10 to the query, the page loads super fast!

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The purpose of the SQL query is to get only the latest data from the table discord . Since the data will only update every 15 minute, the query will easily pick up the latest data.

The relationship with discord and discord_users is that discord needs the ID from discord_users in order to get the information from an user.

To answer symcbean's questions futhermore:

Q) Why, when you are aapparently restricting the ouput to a single record based on the content of the "many" side of the relationship, are you ordering by the "one" side?

A) What do you mean?

Q) Why are you opening 2 cursors on the discord_users table in the absence of differential indexes on the table?

A) Once again, what do you mean? :)

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So here's my question. How can I optimize my SQL query so it dosen't takes almost 1 minute to load the page? Here's a link to the page: https://erik-edgren.nu/discord

Answer 1

If you still have the issue try this option. Create an INDEX say eg index_datelog on the column datetime_logged of discord table. And then try below query

SELECT 
    d.id AS id_d, d.id_user AS id_du, d.id_channel AS id_dc, d.datetime_logged AS logged 
FROM 
    discord d 
JOIN 
    discord_users du ON d.id_user = du.id USE INDEX(index_datelog))
WHERE 
    d. datetime_logged = (SELECT MAX(datetime_logged) FROM discord)
ORDER BY d.datetime_logged ASC