MySQL - Join & Count rows from another table

Question

I have 3 tables, like:
parent(id, name)
children(id, data, parent_id, timestamp)
table_votes(id, user_id, child_id)

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Answer 1

There are few possible options, one of them:

SELECT * ,
  (SELECT count(*)
   FROM `table_votes`
   WHERE `children`.`id` = `table_votes`.`child_id`) AS `Count`
FROM `children`
WHERE `parent_id` = 20

You can use your query as well, but will have to add GROUP BY:

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