如何纠正INNER JOIN中的“重复”计数？

Question

我有一个关于这个查询复制COUNT：

SELECT 
DATE(dia.DTM) AS 'Dia', 
COUNT(temp.TMP) AS 'Index' 
FROM dados_meteo dia 
INNER JOIN dados_meteo temp 
ON temp.DTM = dia.DTM 
AND temp.TMP BETWEEN 20 AND 30 
WHERE dia.POM = 'Alcobaca' 
GROUP BY DATE(dia.DTM) 

Answer 1

如果我理解正确的（请描述exacly你想要查询），您可以通过将INNER JOIN更改为LEFT JOIN来获得所需内容。

或本：

SELECT 
    DATE(dia.DTM) AS 'Dia', 
    SUM(dia.TMP BETWEEN 20 AND 30) AS 'Index' 
FROM dados_meteo dia 
WHERE dia.POM = 'Alcobaca' 
GROUP BY DATE(dia.DTM) 

什么上面的查询实际上做的是这样的：

SELECT 
    DATE(dia.DTM) AS 'Dia', 
    COUNT(CASE WHEN dia.TMP BETWEEN 20 AND 30 
       THEN 'yes' 
       ELSE NULL 
      END) 
     AS 'Index' 
FROM dados_meteo dia 
WHERE dia.POM = 'Alcobaca' 
GROUP BY DATE(dia.DTM) 

---

的意见后，这里有一个轻微的修改：

SELECT 
    DATE(dia.DTM) AS 'Dia', 
    CASE WHEN SUM(dia.TMP BETWEEN 20 AND 30) >= 24 
     THEN 20 
     ELSE -10 
    END AS 'Index' 
FROM dados_meteo dia 
WHERE dia.POM = 'Alcobaca' 
GROUP BY DATE(dia.DTM) 

Answer 2

我更新了查询，但我真的建议有一个单独的日历表：

select "Dia", "Index" 
from 
    (select distinct date(dia.dtm) calendar_date 
    from dados_meteo) calendar left outer join 
    (select date(dtm) as "Dia", count(tmp) as "Index" 
    from dados_meteo 
    where pom = 'Alcobaca' and tmp between 20 and 30 
    group by date(dtm)) temp on calendar.calendar_date = "Dia"