SQL Server Compact（SqlCe 4.0）GROUP BY查询优化

Question

I have a table Invoices

Structure of Invoices

CREATE TABLE Invoices (
  Id               int NOT NULL IDENTITY (1, 1),
  Depot            nvarchar(100) NOT NULL,
  InvoiceNo        nvarchar(100) NOT NULL,
  InvoiceDate      datetime NOT NULL,
  Licencee         nvarchar(255) NOT NULL,
  Outlet           nvarchar(1024) NOT NULL,
  SerialNo         int NOT NULL,
  ProductName      nvarchar(500) NOT NULL,
  Size             int NOT NULL,
  [Case]           int NOT NULL,
  BeverageSegment  nvarchar(100),
  /* Keys */
  PRIMARY KEY (Id)
)
GO

CREATE INDEX Invoices_BeverageSegment
  ON Invoices
  (BeverageSegment)
GO

CREATE INDEX Invoices_InvoiceId
  ON Invoices
  (InvoiceNo)
GO

I have to query for Total Sales for a particular Depot , for a Product on Date , i have approx 1,35,850 in the Table, the Query is taking 47 minute.

I do not have much expertise in database system, i have checked for Query Optimization for SqlCe but none of them helps in this condition.

My query :

SELECT 
  Depot, 
  InvoiceDate, 
  ProductName, 
  Size, 
  SUM([Case]) as Cases 
FROM Invoices 
GROUP BY 
  Depot, 
  InvoiceDate, 
  ProductName, 
  Size

Answer 1

Creating a non clustered index on all the four columns Depot, InvoiceDate, ProductName, Size will increase the performance.

   Create NonClustered Index Index_Name
   on 
   Invoices ( Depot, InvoiceDate,  ProductName, Size)