Question

我是LINQ的新手，正在尝试将SQL子查询转换为lINQ。我们可以在LINQ中编写像SQL这样的子查询吗？

这是数据库

Table EMP                                                                                                  
Name       Null?         Type

EMPNO      NOT NULL      NUMBER(4)
NAME                    VARCHAR2(10)
JOB                     VARCHAR2(9)
MGR                     NUMBER(4)
HIREDATE                DATE
SAL                     NUMBER(7,2)
COMM                    NUMBER(7,2)
DEPTNO                  NUMBER(2)


Table Dpt
Name        Null?        Type
DEPTNO      NOT NULL NUMBER(2)
DNAME                VARCHAR2(14)
LOC                  VARCHAR2(13)

这是SQL查询

SELECT *
FROM emp
WHERE deptno IN (SELECT deptno
                 FROM dept
                 WHERE dname = 'RESEARCH');

这是我的努力：

var r = (from query in conn.EMPs
         where (query.DEPTNO == (from q in conn.DEPTs 
                                 where q.DNAME == "RESERCH"
                                 select q.DEPTNO)) 
         select new
         {
          query
         }).ToList();

Answer 1

我喜欢使用联接：

var r = (from query in conn.EMPs
        join q in conn.DEPTs on query.deptno equals q.DEPTNO 
        select new { query = query, q = q})
        .Where(x => x.q.DNAME == "RESEARCH")
        .ToList();

Answer 2

var departmentNos = dept.Where（dpt => dpt.dname =='RESEARCH'）。Select（dptNo => dptNo.deptno）;

var employee = emp.Where（e => departmentNos.Contains（e.deptno））;

员工才是最终结果。

将SQL子查询转换为LINQ

2 个答案: