c# – 如何在我们在sql中使用的linq中使用左连接？

如何在 Linq中使用Left join来编写SQL查询？

select 
    p.Name,p.Family,E.EmployTypecode,E.employtypeName,E.EmplytyppeTye 
from 
    personnel as p
left join 
    Employee as E on E.EmployTypecode = p.EmployTypecode

解决方法

使用Join关键字而不是Left join,必须使用“INTO”关键字和“DefaultIfEmpty()”方法,因为右表返回null值.

var query = from p in personnel 
               join e in Employee on p.EmployTypecode equals e.EmployTypecode into t
               from nt in t.DefaultIfEmpty()
               orderby p.Name

    select new
    {
        p.Name,EmployTypecode=(int?)nt.EmployTypecode,// To handle null value if Employtypecode is specified as not null in Employee table.
        nt.employtypeName,nt.EmplytyppeTye
    }.ToList();