Question

我有一个执行内部SELECT的MySQL语句，并将结果作为伪列返回。我想在我的WHERE子句中使用这个伪列的结果。我当前的SQL语句如下所示：

SELECT
    product.product_id,
    product.range_id,
    product.title,
    product.image,
    product.image_text,
    product.friendly_url,
    attribute.comfort_grade_id,
    category.category_id,
    category.category AS category_name,
    category.friendly_url AS category_friendly_url,
    (SELECT price_now FROM product_bedding_sizes AS size WHERE size.product_id = product.product_id ORDER BY size.price_now ASC LIMIT 1) AS price
FROM
    products AS product
LEFT JOIN
    categories AS category ON product.category_id = category.category_id
LEFT JOIN
    product_bedding_attributes AS attribute ON product.product_id = attribute.product_id
$where
$order
LIMIT
    ?,?

但是，运行查询时出现以下错误消息：

＃1054 - 'where子句'中的未知列'价格'

如何解决这个问题，并在我的price子句中实际使用WHERE的值？

Answer 1

WHERE子句在SELECT子句之前计算，因此它不会说别名。您必须通过外部查询中的WHERE子句执行过滤，如下所示：

SELECT *
FROM
(
    SELECT
        product.product_id,
        product.range_id,
        product.title,
        product.image,
        product.image_text,
        product.friendly_url,
        attribute.comfort_grade_id,
        category.category_id,
        category.category AS category_name,
        category.friendly_url AS category_friendly_url,
        (SELECT price_now 
         FROM product_bedding_sizes AS size 
         WHERE size.product_id = product.product_id 
         ORDER BY size.price_now ASC 
         LIMIT 1) AS price
    FROM
     ...
) AS sub
WHERE price = ... <--- here it can see the price alias.

有关详细信息，请参阅此处：

My SQL Query Order of Operations。

或：您可以加入该表，而不是像这样的相关子查询：

SELECT
    product.product_id,
    product.range_id,
    product.title,
    product.image,
    product.image_text,
    product.friendly_url,
    attribute.comfort_grade_id,
    category.category_id,
    category.category AS category_name,
    category.friendly_url AS category_friendly_url,
    size.price_now 
FROM
    products AS product
LEFT JOIN
(
   SELECT product_id, MIN(price_now) AS price
   FROM product_bedding_sizes
   GROUP BY product_id
) AS size ON size.product_id = product.product_id
LEFT JOIN
    categories AS category ON product.category_id = category.category_id
LEFT JOIN
    product_bedding_attributes AS attribute ON product.product_id = attribute.product_id
$where price = ----;

Answer 2

尝试使用变量：

@price:= (SELECT price_now 
          FROM product_bedding_sizes AS size 
          WHERE size.product_id = product.product_id 
          ORDER BY size.price_now ASC LIMIT 1) AS price;

然后将其引用为

WHERE @price > 9000;

Answer 3

如果你有

 WHERE price > 0 AND price` <= 199`

在你的where子句中

然后尝试使用HAVING子句

像那样

 $HAVING
      //-- where $having  = HAVING price > 0 AND price <= 199

通过内部选择的结果过滤MySQL结果集

3 个答案: