如何获取MySQL中的关系表中的项目数

Question

i have two mysql db tables 'tags' and 'tags_used'. i have added images for checking the db structure.currently iam using laravel fluent query builder. Now what i want to query is the count of rows in relation table like below. Please help me with either laravel fluent query or plain sql query.

id    | name  |times_used
------------
1 | tag1 | 3
------------
2 | tag2 | 1
------------
3 | tag3 | 5
------------
4 | tag4 | 1
------------
5 | tag5 | 0
------------
----------

Answer 1

Use a LEFT JOIN between the tables, and COUNT() to count the matches.

SELECT t.id, t.name, IFNULL(COUNT(u.id), 0) AS times_used
FROM tags AS t
LEFT JOIN tags_used AS u ON t.id = u.tags_id
GROUP BY t.id

Note that you have to use COUNT(u.id) rather than COUNT(*) so you don't count the row with null values in the tags_used columns when there's no matches.