mysql在一个命令中选择id和count？

Question

使用Mysql如何将这两个命令合并为一个？

select id from User where name='name'
select count(*) from Msg where user_id=@id

Answer 1

您可以加入表格：

SELECT COUNT(*)
FROM User a
INNER JOIN Msg b ON a.id = b.user_id
WHERE a.name = 'name'