Question

我正在尝试找到一种方法来从数据库查询中的结果创建计算，以提供一种相关性。

以下是我的查询示例：

SELECT d.id, MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE) as r_matches, s.total_matches
FROM days d
LEFT JOIN condition_days r
    ON (d.id = r.day_id AND MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE))
LEFT JOIN (SELECT ss.day_id, COUNT(DISTINCT ss.condition_id) as total_matches FROM conditions ss WHERE ss.condition_id IN (4, 13, 20) GROUP BY ss.day_id) s
ON (s.day_id = d.id)

返回的内容如下：

+-----+-----------+---------------+
| id  | r_matches | total_matches |
+-----+-----------+---------------+
| 540 |         2 |             5 |
+-----+-----------+---------------+

所以我的问题是，如何计算2个计算字段（r_matches和total_matches）？这是我正在寻找的一个例子：

+-----+-----------+---------------+----------------------------------------------+
| id  | r_matches | total_matches | total                                        |
+-----+-----------+---------------+----------------------------------------------+
| 540 |         2 |             3 | 5 (calculation of total_matches + r_matches) |
+-----+-----------+---------------+----------------------------------------------+

那么有没有办法从2个计算字段中获得计算总数？

Answer 1

无法在没有模式的情况下测试运行，但使用临时变量这样的事情应该可以正常运行;

SELECT 
  d.id, 
  @tmp := (MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE)) as r_matches, 
  s.total_matches,
  s.total_matches + @tmp AS total
FROM days d
LEFT JOIN condition_days r
  ON (d.id = r.day_id AND MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE))
LEFT JOIN (
  SELECT ss.day_id, COUNT(DISTINCT ss.condition_id) as total_matches 
  FROM conditions ss WHERE ss.condition_id IN (4, 13, 20) GROUP BY ss.day_id) s
ON (s.day_id = d.id)

Answer 2

您可以使用派生表：

   select id, r_matches, total_matches, r_matches + total_matches as total
   from (
       select d.id,
              MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE) as r_matches,
              s.total_matches as total_matches
       ...
   ) as dt;

查询引擎可能足够智能，只计算一次MATCH，即使它被提及两次，所以简单的方法：

select d.id, 
       MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE) as r_matches, 
       s.total_matches,
       MATCH (r.text) AGAINST('sleet snow rain' IN BOOLEAN MODE) + s.total_matches as total
...

可能会正常工作。我不知道MySQL是否会识别重复的MATCH。

选择每行的计算

2 个答案: