如何纠正“内部联接”中的“重复”计数？

问题描述

| 我在此查询中有重复的“ 0”：

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)

    

解决方法

        如果我理解正确（请准确描述您要查询执行的操作），则将

INNER JOIN

更改为

LEFT JOIN

，您将获得所需的内容。 或以此：

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)

上面的查询实际在做什么是这样的：

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)

评论后，这里稍作修改：

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)

    ,        我更新了查询，但我真的建议您使用单独的日历表：

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\"