MYSQL Delete From Based on Multiple Distinct Columns - php

Question

I have this problem that's been killing me for a couple days now.
So we have a table of all processed orders.
We have a table for all orders that come in.
We need to effectively cross-reference the orders in the new table that is continually updating against the orders already completely in the primary table so that we don't complete the same order multiple times.
After we get a batch of new orders, this is the query that I currently run in an attempt to cross reference it with the table of completed orders:
$sql = "DELETE
FROM
`orders_new`
WHERE
`order` IN (
SELECT DISTINCT
`order`
FROM
`orders_all`
)
AND `name` IN (
SELECT DISTINCT
`name`
FROM
`orders_all`
)
AND `jurisdiction` IN (
SELECT DISTINCT
`jurisdiction`
FROM
`orders_all`
)";
As you can probably tell, I want to delete rows from the "orders_new" table where a row with the same order, name, and jurisdiction already exists in the "orders_all" table.
Is this the right way to handle this sort of query?

Answer 1

Well, the right way depends on many things.
But first, I do not like your division into two tables. In that case I would introduce a column identfying state, that woul reference a table with possible states. Those would be "new", "in process", "completed". That way you have one order stored as only one record as it should be.
But your query migt be ok, but you should check the performance.
Take a look at: https://sqlperformance.com/2012/12/t-sql-queries/left-anti-semi-join
Not exactly your case but very similar.
Another thing: Why do you use DISTINCT. That would imply that "order" is not a unique identifier.
Based on your edit you identify the order with composite key "order", "name", "jurisdiction". Is this really the key, the whole key and nothing but the key so help you Codd. If not, you could delete a bunch of records. But even so your query would delete an all orders for which the order, name and jurisdiction can be found in table order IN DIFFERENT RECORDS. So your query is false.
Saying that, a variant of your query might be
DELETE order_new
FROM
order_new
INNER JOIN
order_all ON order_all.order = order_new.order
AND order_all.name = order_new.name
AND order_all.jurisdiction = order_new.jurisdiction
But, the real problem is your ER model.

Answer 2

No, your query will delete any record where there are any records with the same order, name, and jurisdiction, even if those records are different from one another. In other words, a row in orders_new will be deleted if one row in order_all has the same order, a different one has the same name, and a third one has the same jurisdiction. You are very very likely to delete way more than you want to. Instead, this would be more appropriate:
DELETE FROM `orders_new`
WHERE (`order`, `name`, jurisdiction`) IN (
SELECT `order`, `name`, `jurisdiction`
FROM `orders_all`
)
or maybe
DELETE FROM `orders_new`
WHERE EXISTS (
SELECT 1
FROM `orders_all` AS oa
WHERE oa.`order` = `orders_new`.`order`
AND oa.`name` = `orders_new`.`name`
AND oa.`jurisdiction` = `orders_new`.`jurisdiction`
)

Answer 3

You should convert that to a DELETE - JOIN construct like
DELETE `orders_new`
FROM `orders_new`
INNER JOIN `orders_all` ON `orders_new`.`order` = `orders_all`.`order`
AND `orders_new`.`name` = `orders_all`.`name`
AND `orders_new`.`jurisdiction` = `orders_all`.`jurisdiction`;