丢弃具有空值或空的表/子查询

Question

我在PostgreSQL中有这样的视图。：

SELECT met1.tiempo,
    met1.pyrseg AS met1_pyrseg,
    met1.pyrhor AS met1_pyrhor,
    met2.pyrseg AS met2_pyrseg,
    met2.pyrhor AS met2_pyrhor,
    met3.pyrseg AS met3_pyrseg,
    met3.pyrhor AS met3_pyrhor
FROM      
    (SELECT meteo_hour.tstamp AS tiempo,
        avg(meteo_hour.avg_globalradiation1) AS pyrseg,
        avg(meteo_hour.avg_globalradiation2) AS pyrhor
    FROM dw.meteo_hour
    WHERE meteo_hour.meteo = 0
    GROUP BY meteo_hour.tstamp) met1,

    (SELECT meteo_hour.tstamp AS tiempo,
        avg(meteo_hour.avg_globalradiation1) AS pyrseg,
        avg(meteo_hour.avg_globalradiation2) AS pyrhor
    FROM dw.meteo_hour
    WHERE meteo_hour.meteo = 25
    GROUP BY meteo_hour.tstamp) met2,

    (SELECT meteo_hour.tstamp AS tiempo,
        avg(meteo_hour.avg_globalradiation1) AS pyrseg,
        avg(meteo_hour.avg_globalradiation2) AS pyrhor
    FROM dw.meteo_hour
    WHERE meteo_hour.meteo = 35
    GROUP BY meteo_hour.tstamp) met3

WHERE met1.tiempo = met2.tiempo AND met3.tiempo = met1.tiempo

当3个子查询中的一个失败时，会出现问题。由于有一个子查询没有值，因此最后一个WHERE失败，因为其中一个比较是针对空值。

如果有空值或者为空，我如何丢弃子查询？

Answer 1

您应该使用FULL JOIN。通过其他一些改进，您将获得：

SELECT tiempo, met1_pyrseg, met1_pyrhor,
               met2_pyrseg, met2_pyrhor,
               met3_pyrseg, met3_pyrhor
FROM (
    SELECT tstamp AS tiempo,
           avg(avg_globalradiation1) AS met1_pyrseg,
           avg(avg_globalradiation2) AS met1_pyrhor
    FROM dw.meteo_hour
    WHERE meteo = 0
    GROUP BY tstamp) met1
FULL JOIN (
    SELECT tstamp AS tiempo,
           avg(avg_globalradiation1) AS met2_pyrseg,
           avg(avg_globalradiation2) AS met2_pyrhor
    FROM dw.meteo_hour
    WHERE meteo = 25
    GROUP BY tstamp) met2 USING (tiempo)
FULL JOIN (
    SELECT tstamp AS tiempo,
           avg(avg_globalradiation1) AS met3_pyrseg,
           avg(avg_globalradiation2) AS met3_pyrhor
    FROM dw.meteo_hour
    WHERE meteo = 35
    GROUP BY tstamp) met3 USING (tiempo)
ORDER BY tiempo;