How to get certain posts in wordpress - wordpress

Question

I want to implement a function to get certain posts in wordpress.
INPUT
page_number
category_name
VARIABLE
items_per_page = 10
OUTPUT
posts array, like the result of the query_posts() function.
Here is my code:
$page_number = $_GET["page_number"]
$category_name = $_GET["category_name"]
function app_get_posts($page_number, $category,$items_per_page = 10)
{
global $wpdb;
$select ="SELECT POSTS FROM wp_posts WHERE CATEGORY = ".$category." LIMIT (".$page_number." - 1) * ".$items_per_page.",".$page_number." * ".$items_per_page; //it didn't work.
return $wpdb->query($select);
}
When I call the function app_get_posts('2','tech'), it will return the 10th~19th posts in the "tech" category, when I call app_get_posts('3','wordpress'), it will return the 20th~29th posts in the "wordpress" category.
So I am wondering if there is a way to figure out this problem.
Thx in advence.

Answer 1

I guess the reason why the above won't work is because the wp_posts table not has a CATEGORY or POSTS field. I modified you code so you can return posts based on taxonomy:
function app_get_posts($page_number, $category,$items_per_page = 10)
{
global $wpdb;
$start = ($page_number-1) * $items_per_page;
$select ="SELECT DISTINCT wp.* FROM wp_posts wp
INNER JOIN wp_term_relationships rs ON rs.object_id = wp.ID
INNER JOIN wp_terms t ON t.term_id = rs.term_taxonomy_id
WHERE t.name = ".$category." LIMIT ".$start.",".$items_per_page;
return $wpdb->query($select);
}