我有一个存储函数需要 select ... from ... where foo IN (select ...) 问题是，与做一个简单的 where = ... 既然这种语法很慢，有没有可能将结果存储到一个变量中，然后在 IN () 而不是条件？我不知道如何将包含多行的查询存储到一个变量中。
这是使用变量的快速等式(但错误的b/c它只执行1个值而不是多个值）

BEGIN

    DECLARE average DECIMAL(10,4);
    DECLARE skuAsin VARCHAR(30);

    SET skuAsin = (SELECT DISTINCT asin FROM inventory WHERE sku = aSku ORDER BY id DESC LIMIT 1);

    SET average = (
        SELECT  avg(unitsByDay) FROM (
            SELECT i.date, sum(units_ordered) as unitsByDay from inventory i
            WHERE
                i.asin = skuAsin &&
                i.marketplace_id = mid &&
                i.date between d1 and d2
            GROUP BY date
        ) as vel
    );

    RETURN average;

END;

这就是慢用 IN (select) ```
BEGIN

DECLARE average DECIMAL(10,4);

SET average = (
    SELECT  avg(unitsByDay) FROM (
        SELECT i.date, sum(units_ordered) as unitsByDay from inventory i
        WHERE
            i.asin IN (SELECT DISTINCT asin FROM inventory WHERE sku = aSku) &&
            i.marketplace_id = mid &&
            i.date between d1 and d2
        GROUP BY date
    ) as vel
);

RETURN average;

END;