what is best alternate query for this one

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i have a query that is full filling my requirement ,but problem is that when data in that table will increase then it will consume more time ,i want to alternate query in EF so that i will not get that chance. my query is as follow:

C#

var ranks = _service.GetAllEmployeeDuty().OrderByDescending(x => x.EndDate).GroupBy(x => x.Employee_Id).Select(x => x.First()).Where(x => x.ToSector_Id == sectorId).ToList();

Posted 23-Apr-15 20:03pm

Sajid227

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2 solutions

Solution 1

I will always suggest, use group by and order by in last

Posted 23-Apr-15 20:12pm

pankajrawat

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Pascal Ganaye · Accepted Answer · 2015-04-23T20:32:00

You say "when data in that table will increase then it will consume more time"

This is not necessarily as bad as you think.
It really depends of the Linq provider.

Let me explain.
When you execute this query, the engine is not going to run it sequentially in this order:
1 - GetAllEmployeeDuty()
2 - OrderByDescending(x => x.EndDate)
3 - GroupBy(x => x.Employee_Id)
4 - Select(x => x.First())
5 - Where(x => x.ToSector_Id == sectorId)
6 - ToList();

On the contrary linq will only build an expression tree, then transform this expression tree into a big SQL request and pass it to the SQL engine.
The SQL speciality is to estimate which path is faster.
The SQL optimization engine will probably start with the smallest tables and can even change its strategy depending on the number of records in each tables.

In summary, again, this is not necessarily as bad as you think.