Linq to SQL / filter duplicates

问题

i have a view in my sql server 2012 with a couple of duplicates and i want to sort them by the newest and filter all others - can anyone help me?

My viewin my SQL Server 2012:

GUID (as primary key), number, datetime and name

+-----+----------+--------------------------------+-----
| guid  |  number| datetime                       | name
+-----+----------+--------------------------------+------
| b105..| 1234567|2014-07-07T16:32:20.854+02:00:00|Name1
| s1b5..| 1111222|2014-07-06T16:30:21.854+02:00:00|Name2
| b17a..| 1234567|2014-07-06T15:22:17.854+02:00:00|Name1
| f205..| 1233333|2014-07-07T17:40:20.854+02:00:00|Name3
| b11t..| 1233333|2014-07-04T11:12:15.854+02:00:00|Name3
| rt85..| 1111222|2014-07-07T21:55:52.854+02:00:00|Name2
+-------+--------+--------------------------------+-----

the name is every time the same if the number is the same. for e.g. number 1234567 is always name 1.

I want to filter my table that i have only the newest number without duplicates

so the result should be:

+-----+----------+--------------------------------+-----
| guid  |  number| datetime                       | name
+-----+----------+--------------------------------+------
| b105..| 1234567|2014-07-07T16:32:20.854+02:00:00|Name1
| f205..| 1233333|2014-07-07T17:40:20.854+02:00:00|Name3
| rt85..| 1111222|2014-07-07T21:55:52.854+02:00:00|Name2
+-------+--------+--------------------------------+-----

How can i do this in Linq? "Distinct" is not working because of the guid and the datetime

回答1:

var res = list.GroupBy(c => c.name).Select(group => group.OrderBy( c1 => c1.datetime).First()).ToList();

This should work as long as datetime is stored as an instance of DateTime, instead of string.

回答2:

You can do it by grouping your elements by 2 columns. (number and name). Then access the grouped data. You can do it somehow like that:

var query =
        from col in viewData
        group col by new
    {
        col.name,
        col.number,

    } into groupedCol
    select new viewData()
    {
        number = groupedCol.Key.number,
        name = groupedCol.Key.name,
        datetime = groupedCol.OrderBy( dateCol => dateCol.datetime).First()

    };

来源：https://stackoverflow.com/questions/24790715/linq-to-sql-filter-duplicates

标签

sql

linq

filter

sql-server-2012