How to select distinct data from DataBase with LINQ To SQL and have a good performance ?

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Hi Guys,

I want to get the data from database by LINQ TO SQL FIle,

In my Student Table, there are three columns :school, department and Name.
I want to select the distinct student's department through the student's school's name that I have known.

My code is :

C#

DataClassesDataContext d = new DataClassesDataContext();

        IQueryable rets = (from p in d.Students
                                              where p.School=="Computer"
                                    select p).Distinct();

But it does not work well ,it will return a heap of data which is not distinct!
What should I do?

Posted 6-May-11 20:08pm

IT-discovery

Updated 6-May-11 22:07pm

Dalek Dave

v2

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Dalek Dave 7-May-11 4:08am

Edited for Grammar and Readability.

2 solutions

Solution 3

Hi it-discovery,

Try to change your code with this one :

IQueryable rets = (from p in d.Students
                   where p.School == "Computer"
                   select p.department).Distinct();

I hope this help,
:)

Posted 7-May-11 1:22am

Michael Waguih

Updated 7-May-11 1:54am

v2

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NuttingCDEF · Accepted Answer · 2011-05-06T20:28:00

Solution 1

How about select p.department rather than just select p.

select p will give you all p's where any of p.school, p.department or p.name differ - so 2 students with different names in the same school / department are distinct - if you just want distinct departments select p.department which will just give you the department.

Posted 6-May-11 20:28pm

NuttingCDEF

Comments

Dalek Dave 7-May-11 4:08am

Good call.

Prasanta_Prince 7-May-11 7:57am

Good one