mysql使用max作为where条件

Question

I got 4 fields

page_id
page_category_id
page_sequence
page_path

For example

record 1

page_id = 1
page_category_id = 22
page_sequence = 1
page_path = "1.jpg"

record 2

page_id = 1
page_category_id = 22
page_sequence = 2
page_path = "2.jpg"

record 3   

page_id = 1
page_category_id = 23
page_sequence = 1
page_path = "23_1.jpg"

record 4
page_id = 1
page_category_id = 23
page_sequence = 2
page_path = "23_1.jpg"


record 5
page_id = 1
page_category_id = 23
page_sequence = 3
page_path = "23_1.jpg"

.. and more records

I want to do a draw statement that

$sql_select = "select page_category_id from my_table where max(page_sequence) < 3";

it will show all the page_category_id who max(page_sequence) is less than 3.

but I can't do it with max(page_sequence) as the where condition

How can I get it working.. Thanks !

Answer 1

select page_category_id from my_table 
GROUP BY page_category_id 
HAVING max(page_sequence) < 2

Answer 2

SQL is such fun, since you can almost always solve things in several completely different ways. Here's a NOT EXISTS alternative:

select distinct page_category_id
from tablename t1
where not exists (select 1 from tablename t2
                  where t2.page_category_id = t1.page_category_id
                    and t2.page_sequence >= 3)

Return a page_category_id if there are no row with same page_category_id that has a page_sequence >= 3.