Join two identical tables on rows with different values

Question

I have two identical tables, one with current values for rows, and one with new values. I am trying to select only the rows from the new values table where any column in the new values table has a different value than the column in the old values table. The query I am using now looks like:

SELECT `new`.`item_id` 
  FROM `new_items` AS `new` 
  JOIN `items`  AS `old` 
 WHERE new.item_id = old.item_id
   AND (new.price != old.price || 
        new.description != old.description || 
        new.description_long != old.description_long || 
        new.image_small != old.image_small || 
        new.image_large != old.image_large || 
        new.image_logo1 != old.image_logo1 )

However, this query takes WAY too long to execute. Does MySQL have a better way to do this or does anyone know a more efficient query?

Answer 1

Use:

SELECT n.item_id
  FROM NEW_ITEMS n
 WHERE EXISTS (SELECT NULL
                 FROM OLD_ITEMS o
                WHERE o.item_id = n.item_id
                  AND (o.price <> n.price
                   OR o.description <> n.description 
                   OR o.description_long <> n.description_long 
                   OR o.image_small <> n.image_small 
                   OR o.image_large <> n.image_large 
                   OR o.image_logo1 <> n.image_logo1))

Index all of the columns being compared.

Answer 2

如果item_id（sku）相当唯一（表中没有很多重复的item_id），那么通过在item_id上添加索引，您将看到性能上的显着提高。