从数据集中检索数据

Question

SqlDataAdapter da = new SqlDataAdapter("Select StudentID,StudentName from StudentMaster where StudentID = '" + start + "'", conn);              
DataSet ds = new DataSet();
da.Fill(ds,"StudentMaster");
SqlDataAdapter db = new SqlDataAdapter("Select Registration_No from Candidate_Registration where StudentID='" + start + "'", conn);
db.Fill(ds, "Candidate_Registration");

Here 'start' is a textbox value of a textbox in previous form ie form2. I want to fetch StudentName and StudentID from StudentMaster where StudentID = start. The table is named 'StudentMaster'. Fill the dataset with StudentMaster. Then I want to fetch Registration_No from Candidate_Registration where StudentID=start. The table is named 'Candidate_Registration'. Fill the dataset with Candidate_Registration. Now according to the 'Registration_No' that is fetched, I want to fetch 'CourseID' from 'Registered_Courses'. But, the problem is, how to access the fetched 'Registration_No' ie how to put it in the following query: if I can take the fetched Registration_No into a variable named 'reg_no' then, "Select CourseID from Registered_Courses where Registration_No="+ reg_no;

For more understanding I mention the tables and the relationships....

StudentMaster
-------------
StudentID Primary key,
StudentName

Candidate_Registration
----------------------
Registration_No Foreign key,
ExamID Foreign key,
StudentID Foreign key,
Seat_No,
Primary key(Registration_No,ExamID)

Registered_Courses
------------------
Registration_No Primary key,
ExamID Foreign key,
CourseID Foreign key,

Course_Master
-------------
CourseID Primary key,
Course_Name,
Description

ie finally I want to get the Course_Name for a particular StudentID.

Can anyone please help me out. Thanks in advance!

Answer 1

Try this query :

Select StudentMaster.StudentId, Course_Master.Course_Name from StudentMaster 
INNER JOIN Candidate_Registration 
ON Candidate_Registration.StudentId = StudentMaster.StudentId 
INNER JOIN Registered_Courses 
ON Registered_Courses.Registration_No = Candidate_Registration.Registration_No AND Registered_Courses.ExamID = Candidate_Registration.ExamID 
INNER JOIN Course_Master 
ON Course_Master.CourseID = Registered_Courses.CourseID
WHERE StudentMaster.StudentId = @MyId

Replace @MyId with your Id parameter and it gives you all the CourseNames for a StudentId.