sql - SQL - 从单独表中的列值中选择记录数

Question

我在这里完全被难住了，我希望我没有忽略其他地方的答案。

我有两张桌子，asset和purchase_order。

资产

asset_key | description | purchase_order_key

采购订单

purchase_order_key | order_number | number_of_assets

我正在尝试获取采购订单列表，每个订单都满足以下条件：

• 具有给定 purchase_order_key 的资产表中的总行数小于具有该 purchase_order_key 的 purchase_order 行中的 number_of_assets 值。

例如，假设该asset表有 4 行相同purchase_order_key(24) 行，17 行不同purchase_order_key(66)。如果purchase_order24 列出 4 number_of_assets，而purchase_order66 列出 19 number_of_assets，则查询应返回purchase_order66，而不是purchase_order24。

Answer 1

您可以使用子查询：

SELECT *
FROM purchase_order
WHERE number_of_assets > (
    SELECT COUNT(*)
    FROM asset
    WHERE asset.purchase_order_key = purchase_order.purchase_order_key
)

Answer 2

您需要COUNT对已assets加入的 PO 表执行一次操作，然后将它们与记录的资产数量进行比较。

SELECT PO.purchase_order_key, COUNT(A.purchase_order_key)
FROM purchase_order PO
    LEFT JOIN asset A ON PO.purchase_order_key = A.purchase_order_key
GROUP BY PO.purchase_order_key, PO.number_of_assets
HAVING COUNT(*) > PO.number_of_assets

Answer 3

我认为这就是你要找的：

SELECT
    PO.*
FROM
    purchase_order PO
    INNER JOIN
        (
            SELECT 
                A.purchase_order_key,
                COUNT(A.asset_key) asset_key_count
            FROM
                asset A
            GROUP BY
                A.purchase_order_key

        ) AC on AC.purchase_order_key = PO.purchase_order_key and AC.asset_key_count < PO.number_of_assets