Optimizing Sub Query Getting Last Entry Based On Group - mysql

Question

We had a bug in our code that cached the wrong values to the last_order_id (expected_previous_order) column. The query I wrote properly finds the correct last order id but is too slow for our data set.
I want to select this data into another table but I cannot because the query will take too long
I have setup a simple example here with a smaller data set. Original table has about 170k rows.
SQL Fiddle of my Example
In the example:
original_artwork_id is how these rows are grouped.
order_id is the current rows order id
actual_previous_order is the corrected last order id
expected_previous_order is the currently stored last order id. This is the wrong value as it does not actually reference the last order id
EXPLAIN Results
EDIT
Every time a reorder is placed a new entry is placed into the order_artwork table with a reference to the original_artwork_id and last_order_id.
The reference in the current data set to the last_order_id is wrong.
I need to update all records to properly indicate the last order id.
I am doing this by trying to find each artwork and joining it with the previous entry of the same original_artwork_id. Then I can pull the order_id from the last entry to update the current entries last_order_id
Join the current row with the previous row created before the current row with the same original_artwork_id or the current row original_artwork_id = the previous rows id

Answer 1

Not sure if this will be faster than your current query. But anyway.
SQL DEMO
First you need add a new field
`pos` int DEFAULT 0,
And update your base case so can do the JOIN.
update `order_artwork` o
SET `original_artwork_id` = `id`
WHERE `original_artwork_id` IS NULL;
You could use COALESCE(original_artwork_id, id) but cant use index on that case.
Then assign a row_number to each order based in original_artwork_id and date
update `order_artwork` o
left join (
SELECT o.id,
#rn := if(#order_id = `original_artwork_id`,
#rn + 1,
if(#order_id := `original_artwork_id`, 1, 1)
) as rn
FROM `order_artwork` o
CROSS JOIN (SELECT #id := 0, #order_id := 0, #rn := 0) as var
ORDER BY `original_artwork_id`,
`created`
) b on
o.id = b.id
set
o.pos = b.rn;
Finally update the last order.
UPDATE `order_artwork` o
JOIN (
SELECT o1.original_artwork_id,
o2.order_id,
o1.order_id as last_order_id
FROM `order_artwork` o1
LEFT JOIN `order_artwork` o2
ON o1.pos = o2.pos - 1
AND o1.original_artwork_id = o2.`original_artwork_id`
WHERE o2.pos IS NOT NULL
) as b
ON o.original_artwork_id = b.original_artwork_id
AND o.order_id = b.order_id
SET o.last_order_id = b.last_order_id;

Answer 2

I found that the created time column was not reliable. So I decided to just find the last highest order id with the same original_artwork_id.
Create a table that has the corrected values
CREATE TABLE order_artwork_two AS
select
d1.id,
d1.order_id,
max(d2.order_id) last_order_id,
d1.original_artwork_id
from order_artwork d1
left join order_artwork d2
ON d1.original_artwork_id = d2.original_artwork_id
and d1.order_id > d2.order_id
group by d1.original_artwork_id, d1.order_id;
Add an index to the new table. Otherwise the update would be way too slow
alter table order_artwork_two add primary KEY(id);
Update our original table.
update order_artwork d1
left join order_artwork_two d2 on d2.id = d1.id
set d1.last_order_id = d2.last_order_id;