As previously stated this is high potential of the issue.
WHERE SD.Code IS NOT NULL AND RTRIM(LTRIM(SD.Code ))<>''
That renders your query nonSARGable. You could change that be simply:
WHERE SD.Code > ''
This will still find any value that is not '' and NULL will already be excluded.
--EDIT--
Had a desk meeting while posting and got pulled away. Seems that Gail already posted much the same as I did. 😛
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