var query = (
from a in station
join b in mic_data on a.ID equals b.ID into joinEmpDept
from x in joinEmpDept.DefaultIfEmpty()
join c in mic_data1 on a.ID equals c.ID into joinEmpDept2
from j in joinEmpDept2.DefaultIfEmpty()
select new
{
a.NAME,
x.NO2,
.......
AQIH = Math.Round((double)((x.AQI - j.AQI) / (j.AQI == 0 ? 1 : j.AQI) * 100), 2)
}
).ToList();
加上null值判断
NO2 = x == null ? 0 : x.NO2,
SO2 = x == null ? 0 : x.SO2,
PM10 = x == null ? 0 : x.PM10,
......
【1】linq左连接参考https://www.cnblogs.com/yxys/p/5895372.html
【2】DefaultIfEmpty()方式输出的null值判断