-1

I need some help with a view.

I have 2 tables that I need to "merge" together.

First table contains info about products (product-color-size), and the other tables has info about stock, sold, avilable (quantity) etc on product-season-color-size niveau.

I need my view to return available pr product. The same product-color-size can be multiple times (It can be on multiple seasons), and therefore I can't just sum on ex available.

My query looks like this

SELECT
    SUM((
        SELECT
            SUM(products_details.available)
        FROM
            products_details
        WHERE
            products_details.product_id = products.id
    )) AS available
FROM
    products

But, this will not work. If one size has 6 in available and another has -5, the query will return 1 available. But, I actually got 6, I can sell.

Therefore I need to do some adjustments

SELECT
    SUM((
        SELECT
            SUM(
                IF(
                    products_details.available > 0,
                    products_details.available,
                    0
                )
            )
        FROM
            products_details
        WHERE
            products_details.product_id = products.id
    )) AS available
FROM
    products

But, this will also not work. If the size has 6 in available on one season, and -5 on another, the query will return 6 available. But, these two rows I need to sum, because it's the same product. Therefore it needs to return 1 available.

So, I came up with

SELECT
    SUM(
        IF(
            (
                SELECT
                    SUM(
                        IF(
                            products_details.available > 0,
                            products_details.available,
                            0
                        )
                    )
                FROM
                    products_details
                WHERE
                    products_details.product_id = products.id
            ) > 0,
            (
                SELECT
                    SUM(
                        IF(
                            products_details.available > 0,
                            products_details.available,
                            0
                        )
                    )
                FROM
                    products_details
                WHERE
                    products_details.product_id = products.id
            ),
            0
        )
    ) AS available
FROM
    products

But, that will be very (!!) slow. Can I somehow use the same subquery multiple times? So I can use it in the If-statement, and if it's positive I can use the same value to use in the sum?

It's pretty complex, but I hope someone can help me

/Mads

Edit

I just found out, that I can write

SELECT
    SUM((
        SELECT
            IF(
                SUM(products_details.available) > 0,
                SUM(products_details.available),
                0
            )
        FROM
            products_details
        WHERE
            products_details.product_id = products.id
    )) AS available
FROM
    products

That could work okay

Edit2

I found a new and much quicker way to write it, and it works just fine :-)

SELECT
    SUM(GREATEST(0,(
        SELECT
            SUM(products_details.available)
        FROM
            products_details
        WHERE
            products_details.product_id = products.id
    ))) AS available
FROM
    products
GROUP BY
    products.id

This is very quick - from about 10 sec to just above 1 sec.

4

1 に答える 1

1

サブクエリは、この仕事に適したツールではありません。実際、日常の SQL クエリでサブクエリが使用されることはほとんどありません。役に立つ可能性が高いのはJOINs です。

SELECT products.*, SUM(IF(product_details.available > 0, product_details.available, 0)) AS available
FROM products
INNER JOIN product_details ON (product_details.product_id = products.id)
GROUP BY products.id

これにより、製品ごとに 1 つの行が返され、 のavailabilityすべての行にわたるその製品のすべての値の合計が返されますproducts_details。

于 2012-07-09T12:45:12.487 に答える