Question

1）我有查询来检索文件的ID，如下所示：

SELECT virtuemart_media_id
FROM __virtuemart_product_medias
WHERE virtuemart_product_id = "1"
ORDER by ordering ASC

这给了我一些想法，比如23,7,8,24，那很好。

然后我需要在另一个WHERE语句中使用上面的值来选择那些文件。所以我有这样的事情：

SELECT file_url, virtuemart_media_id
FROM __virtuemart_medias 
WHERE virtuemart_media_id IN (
    SELECT virtuemart_media_id
    FROM __virtuemart_product_medias
    WHERE virtuemart_product_id = "1"
    ORDER by ordering ASC
)

这也有效，除了我得到的订单文件的结果：7,8,23,24 - 所以不是按顺序23,7,8,24。

问题出在哪里？似乎没有保留内部SELECT的顺序。

Answer 1

这将取代您的两个查询。

SELECT __virtuemart_medias.file_url, __virtuemart_medias.virtuemart_media_id 
FROM __virtuemart_medias INNER JOIN __virtuemart_product_medias ON 
__virtuemart_medias.virtuemart_media_id=__virtuemart_product_medias.virtuemart_media_id WHERE 
__virtuemart_product_medias.virtuemart_product_id = '1' ORDER BY 
__virtuemart_product_medias.ordering ASC

Answer 2

SELECT a.file_url, a.virtuemart_media_id
FROM __virtuemart_medias a
INNER JOIN __virtuemart_product_medias b  ON a.virtuemart_media_id  = b.virtuemart_media_id
ORDER BY b.ordering ASC;

这将有效

Answer 3

IN子句中没有顺序。它只是一组价值观。（1,2,3）中的x与（3,2,1）中的x相同，（1,2,3）中的x与（3,2,1）中的相同。加入表格即可访问您的订购栏：

SELECT vm.file_url, vm.virtuemart_media_id
FROM __virtuemart_medias vm
INNER JOIN __virtuemart_product_medias vpm
  ON vm.virtuemart_media_id  = vpm.virtuemart_media_id
WHERE vpm.virtuemart_product_id = 1
ORDER BY vpm.ordering ASC;

Answer 4

in的子查询可能会产生多个结果。在这种情况下，您必须定义订购所需的那个。

当替换in后跟带有join的子查询时，您需要确保不会意外地乘以记录数。这需要使用聚合或distinct删除重复项：

SELECT m.file_url, m.virtuemart_media_id
FROM __virtuemart_medias  join
     (select virtuemart_media_id, min(ordering) as ordering
      from __virtuemart_product_medias
      where WHERE virtuemart_product_id = 1
      group by virtuemart_media_id
     ) mi
     on m.virtuemart_media_id = mi.virtuemart_media_id
ORDER by mi.ordering ASC;

mysql - 按多个select中的字段排序

4 个答案: