连接同一表中的多列

Question

我正在计算我们技术人员使用的产品数量

桌子的设置像

count1，size1，count2，size 2

$sql="select SUM(count1) AS count1, size1, SUM(count2) AS count2, size2 FROM PARTS WHERE crew='$crew' GROUP BY size1 ORDER BY size1 DESC";

可以，但是显示为两个单独的列，我必须手动将两者加在一起。 当我尝试：

$sql="select SUM(count1) AS count1, size1, SUM(count2) AS count1, size2 AS size1 FROM PARTS WHERE crew='$crew' GROUP BY size1 ORDER BY size1 DESC";

我收到错误：组语句中的列“ size1”不明确。 我该如何进行？

Answer 1

你是这个意思吗？

$sql="select SUM(count1 + count2) AS count, size1 FROM PARTS WHERE crew='$crew' GROUP BY size1 ORDER BY size1 DESC";

Answer 2

假设两个大小列都是可互换的，则可以合并每个零件大小的所有两个查询，然后应用sum计算：

SELECT   size, SUM(cnt)
FROM     (SELECT size1 AS size, count1 AS cnt FROM parts WHERE crew='$crew'
          UNION ALL
          SELECT size2 AS size, count2 AS cnt FROM parts WHERE crew='$crew') t
GROUP BY size
ORDER BY size DESC