MySQL: what is the best way to create access system?

Question

I have table called page which represents every single page in my website.

page_id | page_subject | page_path
----------------------------------
1       | Foo          | /Foo
2       | Bar          | /Bar

I also have table called group:

group_id | group_name
---------------------
1        | Users
2        | Admins

Goal: how to define access to every page for single group? I did create another table - page_group:

page_group | group_id
---------------------
1          | 1
1          | 2

Table contains groups that have access to page (page_group).

I wrote function:

CREATE FUNCTION `PAGE_ACCESS`(`pageId` INT, `groupId` MEDIUMINT)
BEGIN
   RETURN IF((SELECT COUNT(*) FROM `page_group` WHERE page_id = pageId AND group_id = groupId) > TRUE, FALSE);
END;

Now I can do something like that:

SELECT * 
FROM page 
WHERE <conditions> AND PAGE_ACCESS(page_id, <group_id>)

...which returns pages that I should have access to.

Works fine but seems to be slow with with rows > 100,000 How would you do that? Would you do that in a different way?

Answer 1

try:

SELECT * 
from Page p
WHERE EXISTS (SELECT 1 from page_group pg join group g 
              on (pg.group_id = g.groupidId)
              WHERE g.group_id = <groupId>
                AND p.page_id = pg.page_id)

Also you can try (just realized that groups table does not required):

SELECT * 
from Page p
WHERE p.page_id IN (Select page_id
                    from page_group pg
                    WHERE pg.group_id = <group_id>)

or even:

SELECT p.* 
from Page p JOIN page_group pg ON (p.page_id = pg.page_id)
WHERE pg.group_id = <group_id>

Answer 2

I would test the speed of the query with EXPLAIN SELECT - I'm guessing you don't have indexes on the tables? Another speculation: an index on (page_group.page_group,page_group.group_id) might speed things up. See this introduction on EXPLAIN.

In addition, see @Michael Pakhantsov's answer with the subquery - it's easier for the server to optimize a subquery than a UDF.