将参数传递给子查询

Question

我想知道是否可以将参数传递给select子查询。

我想要做的是从一张桌子收集一些产品数据，然后将物品的重量交叉到运输表中的运输成本以返回成本。

类似的东西：

select cataloguenumber, productname, 
      (select shipping.carriagecost 
       from shipping 
       where shipping.carriageweight = weight) as carriagecost
from products

此致

DPERROTT

Answer 1

虽然子查询可以工作，但更好，更易读和有效的方法来定义它将如下：

SELECT  p.cataloguenumber
 ,      p.productname,  
 ,      s.carriagecost    
FROM    products p
    INNER JOIN
        shipping s
    ON  p.weight = s.carriageweight

这假定所有产品重量在装运表中都有相应的条目。如果情况并非如此，则从INNER JOIN更改为LEFT JOIN并处理任何空值。

Answer 2

select cataloguenumber, productname,  shipping.carriagecost as carriagecost 
from products, shipping 
where shipping.carriageweight = products.weight

或者我错过了什么？

Answer 3

SELECT DISTINCT cataloguenumber, productname, shipping.carriagecost 
FROM products
LEFT OUTER JOIN shipping 
ON shipping.carriageweight = products.weight

Answer 4

您的子查询应该只返回1行，如果它返回的更多，则查询将在运行时抛出错误。

Answer 5

我认为这是可能的，但是您应该检索要在父查询中传递的列。

select cataloguenumber, productname, weight 
      (select shipping.carriagecost 
       from shipping 
       where shipping.carriageweight = weight) as carriagecost
from products

Answer 6

SELECT DISTINCT products.cataloguenumber, products.productname, shipping.carriagecost 
FROM products
LEFT JOIN shipping ON shipping.carriageweight = products.weight