mysql别名的未知列问题

Question

当列是创建的别名时,我无法弄清楚为什么我会得到一个未知列.任何帮助都会很棒.

码:

SELECT DISTINCT 
    c.id, 
    ((SUM(c.width_feet)*12)+(SUM(c.width_inches))) AS width, 
    ((SUM(c.height_feet)*12)+(SUM(c.height_inches))) AS height 
    FROM carpets AS c 
    WHERE c.active = '1' 
    AND (width BETWEEN '0' AND '275') 
    AND (height BETWEEN '0' AND '599') 
    ORDER BY c.item_no 

错误:

'where子句'中的未知列'width'

Answer 1

您无法直接按名称访问别名.

一种解决方案是使用子查询中的别名包装查询,然后引用外部查询中的别名:

SELECT DISTINCT * 
FROM 
    (
     SELECT c.id, 
          ((SUM(c.width_feet)*12)+(SUM(c.width_inches))) AS width, 
          ((SUM(c.height_feet)*12)+(SUM(c.height_inches))) AS height
     FROM carpets AS c 
     WHERE c.active = '1'
    ) sub
WHERE (sub.width BETWEEN '0' AND '275') 
AND   (sub.height BETWEEN '0' AND '599') 
ORDER BY sub.item_no

Answer 2

您可以在order by子句中使用别名,但不能在where或group by子句中使用别名.要么重复表达式,要么可以使用子查询.