How To Retrive Maximun Version Related To Post?

I have two tables:

table posts
id
text

table old_posts
id 
post_id
text
version

the relation is one to many between post and old_posts when the user edits his/her post I save the old version in old_posts but I need to increment the version number so I have first to get the maximum version for that post.

how I achieve this?

in this situation, you don't need to use the version column within the database table, instead of that you just need to count the number of the old_post's rows table.

the query should be like below with eloquent:

$versions = Old_post::where('post_id', $post_id)->count();