如何对两个 SUMmed SQL 结果字段求和

Question

我有一个简单的 table 结构保存 reagent_bottles 和 reagent_aliquots 的记录。

等分试样是从瓶子创建的，并且等分试样记录有一个外键，bottle_id，指向一个瓶子 ID。

要获取特定试剂的总体积（计算瓶子中的体积和等分试样中的体积），以下查询完成部分工作：

SELECT  
      COALESCE(SUM(rb.volume), 0) AS bVolume, 
      COALESCE(SUM(ra.volume), 0) AS aVolume
FROM reagent_bottles AS rb
LEFT JOIN 
      reagent_aliquotes AS ra
ON rb.id = ra.bottle_id
WHERE reagent_id = 408;

returns 对于上述试剂 id (408):

bVolume | aVolume
       2|       6

将 bVolume 和 aVolume 相加，是正确答案，即 8。

问题是，我如何重写上述查询以创建新字段 total_volume，在查询中对 bVolume 和 aVolume 求和？

我试过这个：

SELECT  
      COALESCE(SUM(rb.volume), 0) AS bVolume , 
      COALESCE(SUM(ra.volume), 0) AS aVolume, 
      SUM(bVolume + aVolume) AS total_volume
FROM 
      reagent_bottles AS rb
LEFT JOIN 
      reagent_aliquotes AS ra
ON rb.id = ra.bottle_id
WHERE reagent_id = 408;

但出现错误，未知列，字段列表中的 bVolume..!

Answer 1

对原始列求和：

SELECT  
      COALESCE(SUM(rb.volume), 0) AS bVolume , 
      COALESCE(SUM(ra.volume), 0) AS aVolume, 
      SUM(COALESCE(rb.volume, 0) + COALESCE(ra.volume, 0)) AS total_volume
FROM 
      reagent_bottles AS rb
LEFT JOIN 
      reagent_aliquotes AS ra
ON rb.id = ra.bottle_id
WHERE reagent_id = 408;

如何对两个 SUMmed SQL 结果字段求和

How to SUM two SUMmed SQL result fields

mysql

sql

sum

left-join

where-clause