考えられるオプションはいくつかありますが、そのうちの1つは次のとおりです。
SELECT * ,
(SELECT count(*)
FROM `table_votes`
WHERE `children`.`id` = `table_votes`.`child_id`) AS `Count`
FROM `children`
WHERE `parent_id` = 20
クエリも使用できますが、GROUP BY
を追加する必要があります :
SELECT
`children`.`id`,
`children`.`data`,
`children`.`parent_id`,
`children`.`timestamp`,
COUNT(`v`.`children_id`)
FROM `children` LEFT JOIN `table_votes` `v` ON `children`.`id` = `v`.`child_id`
WHERE `children`.`parent_id` = 20
GROUP BY `children`.`id`, `children`.`data`, `children`.`parent_id`, `children`.`timestamp`,
ORDER BY `timestamp` ASC