MySQL：子查询中的值求和

Question

是否可以对子查询中的两个值求和？

我需要选择三个值：total_view，total_comments和rating。

两个子查询都非常复杂，因此我不希望重复。

我的查询示例：

SELECT p.id,
(
    FIRST subquery  
) AS total_view,
(
    SECOND subquery 
) AS total_comments,
(
    total_view * total_comments
) AS rating
FROM products p
WHERE p.status = "1"
ORDER BY rating DESC

Answer 1

我建议使用子查询：

SELECT p.*, (total_view * total_comments) as rating
FROM (SELECT p.id,
             (FIRST subquery) AS total_view,
             (SECOND subquery) AS total_comments,
      FROM products p
      WHERE p.status = '1'  -- if status is a number, then remove quotes
     ) p
ORDER BY rating DESC;

MySQL实现子查询。 但是，由于ORDER BY位于计算列上，因此无论如何都需要对数据进行排序，因此实现不会产生额外的开销。

Answer 2

您不能使用别名，但可以使用相同的代码，例如：

  SELECT p.id,
  (
      FIRST subquery  
  ) AS total_view,
  (
      SECOND subquery 
  ) AS total_comments,
  (
      (
      FIRST subquery  
    ) * (
      SECOND subquery 
    )
  ) AS rating 

  FROM products p
  WHERE p.status = "1"
  ORDER BY rating DESC

Answer 3

只需使用派生表即可重用别名：

SELECT p.id,
   total_view,
   total_comments,
   total_view * total_comments AS rating
FROM
 (
   SELECT p.id,
    (
        FIRST subquery  
    ) AS total_view,
    (
        SECOND subquery 
    ) AS total_comments
    FROM products p
    WHERE p.status = "1"
 ) as dt
ORDER BY rating DESC