Self Join

SELECT 
    i1.item_name AS item_name,
    i2.item_name AS related_item_name,
    ic.item_category_name
FROM 
    items i1
JOIN 
    items i2
    ON i1.item_category_id = i2.item_category_id
    AND i1.item_id < i2.item_id
JOIN 
    item_categories ic
    ON i1.item_category_id = ic.item_category_id;