String.Join v SQL

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DECLARE @Codes VARCHAR(8000) 
SELECT @Codes = COALESCE(@Codes + ', ': '') +  tdefSymptomCode.SymptomCodeNumber
    FROM  RMA INNER JOIN
        trelRMA_SymptomCode ON RMA.IdRMA = trelRMA_SymptomCode.fiRMA INNER JOIN
        tdefSymptomCode ON trelRMA_SymptomCode.fiSymptomCode = tdefSymptomCode.idSymptomCode
    where idRMA=2
    order by SymptomCodeNumber
return @Codes