You have no indexes on DRTemp that support that query.

Add an index (CUSTNO, DRDATE) INCLUDE (ID)

This index is likely useless

CREATE NONCLUSTERED INDEX [IX_DRTemp] ON [dbo].[DRTemp]

(

[ID] ASC,

[DRNo] ASC,

[CustNo] ASC

)

It has the same leading column as the clustered index, with a wider key. Drop it. Any queries that use it can use the clustered index.

I would also suggest that you drop this:

CONSTRAINT [IX_DRSummTemp] UNIQUE NONCLUSTERED

(

[DRID] ASC,

[StyleNo] ASC

)

and replace it with

CREATE UNIQUE NONCLUSTERED INDEX IX_DRSummTemp

ON DRSummTemp

(

[DRID] ASC,

[StyleNo] ASC

)

INCLUDE (Quantity, Cost)