在查询时将变量设置为true或false

Question

I'm in a bit of a dilemma here and would appreciate opinions

I have the following schema

User{id,name}
Class{id}
textbook{id,name,public}
class_textbook{id,class_id,textbook_id}
class_membership{id,user_id,class_id}

textbook.public is a boolean field marking if a textbook is available for download by every student or only by students participating in a class to which the book is assigned

I want to select every textbook which is available to the user (either public or assigned in a class the user participates) but I have to know which book is public, which isn't and which class is taught with a public textbook.

One way to solve this is by running two queries One to get every textbook available to the user and one to find the public ones

Or i could define a mysql function to do this for me.

Answer 1

SELECT 
    * 
FROM textbook 
WHERE id in (SELECT textbook_id FROM class_textbook WHERE class_id IN (SELECT class_id FROM class_membership WHERE user_id = :user_id)) 
   OR public = true

where :user_id is the id number associated with the user in question.