CODEWITHSUNDEEP
mysqlnested
Ted S
Ted S

Reputation: 337

mySQL Nested Update using COUNT/MIN/MAX from another Table

I have two large tables, products (500k records) and store_products (> 3mm records). Products is the master and product_stores is individual locations with the product.

I need to run a single QUERY totaling up information from product_stores and updating the corresponding product.

When this was smaller dataset we did it with a nested query:

SELECT productid,COUNT(id) as count,MIN(price) as lowprice,MAX(price) as highprice FROM store_products
WHILE (productid){ update product set stores = count, min = lowprice, max = highprice WHERE productid = $productid }
GROUP BY productid

I'm fairly new to nested updates and uncertain how to set multiple fields with a join and group by.

Structure [truncated to relevant fields]:

CREATE TABLE product ( 
product_id INT UNSIGNED NOT NULL AUTO_INCREMENT,     
stores INT UNSIGNED NOT NULL DEFAULT '0',    
lowprice DECIMAL (6,2) NOT NULL DEFAULT '000.00', 
highprice  DECIMAL (6,2) NOT NULL DEFAULT '000.00', 
PRIMARY KEY (product_id), 
KEY stores (stores) 
)

CREATE TABLE store_product (
id INT UNSIGNED NOT NULL AUTO_INCREMENT,    
product_id INT UNSIGNED NOT NULL,
price DECIMAL(7,2) NOT NULL DEFAULT '0.00',
PRIMARY KEY (storeproduct_id),
KEY product_id (product_id)
);

Fields to update:

Upvotes: 2

Views: 1709

Answers (1)

Tom Mac
Tom Mac

Reputation: 9853

Running a single query to perform the update on tables of this size will probably take a while. Anyway - the following should give you what you need. The trick is to alias the product table and then reference the product table in the subselect using that alias. So:

update product p 
set p.lowprice = (select min(price) from store_product sp where sp.product_id = p.product_id),
    p.highprice = (select max(price) from store_product sp where sp.product_id = p.product_id),
    p.stores = (select count(*) from store_product sp where sp.product_id = p.product_id)
where product_id in (select sp.product_id from store_product sp);

One gotcha here is that the stores column will not be updated to 0 for rows that are not present in the store_product table. To cater for this you can use IFNULL while performing a global update:

update product p
set lowprice = ifnull((select min(price) from store_product sp where sp.product_id = p.product_id),0),
    highprice = ifnull((select max(price) from store_product sp where sp.product_id = p.product_id),0),
    stores = ifnull((select count(*) from store_product sp where sp.product_id = p.product_id),0);

You may want to try both out and see which is faster.

Hope this helps!

Upvotes: 4

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