genome strings comparisons, Sql Server

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DECLARE @myTable TABLE 
(
     SubjectID VARCHAR(MAX), 
     country VARCHAR(MAX), 
     gene VARCHAR(MAX), 
     position INT, 
     RefGenome VARCHAR(1), 
     TestGenome VARCHAR(1), 
     codon INT, 
     nucleotide_order INT 
)

INSERT INTO @myTable 
VALUES
('1-0002','India','gyrA',   65,'A','x', 92,1),
('1-0002','India','gyrA',   66,'T','x', 92,2),
('1-0002','India','gyrA',   67,'C','C', 92,3),
('1-0002','India','gyrA',   68,'T','T', 93,1),
('1-0002','India','gyrA',   69,'A','A', 93,2),
('1-0002','India','gyrA',   70,'C','C', 93,3),
('1-0002','India','gyrA',   71,'G','G', 94,1),
('1-0002','India','gyrA',   72,'A','A', 94,2),
('1-0002','India','gyrA',   73,'C','C', 94,3),
('1-0002','India','gyrA',   74,'A','A', 95,1),
('1-0002','India','gyrA',   75,'G','C', 95,2),
('1-0002','India','gyrA',   76,'C','C', 95,3),
('1-0002','India','gyrA',   77,'C','C', 96,1),
('1-0002','India','gyrA',   78,'T','T', 96,2),
('1-0002','India','gyrA',   79,'G','N', 96,3)

select SubjectID, country, gene, codon, case when RefGenomeStr = TestGenomeStr then 'WT' else TestGenomeStr end wanted_string
from @myTable t1
cross apply(
    SELECT
        STUFF((
              SELECT
                    ', ' +RefGenome
              FROM @myTable t2
              WHERE t2.SubjectID= t1.SubjectID and t2.country = t1.country and  t2.gene = t1.gene and t2.codon = t1.codon
              FOR XML PATH ('')
              )
             , 1, 1, '')
      , STUFF((
              SELECT
                    ', ' +TestGenome
              FROM @myTable t2
              WHERE t2.SubjectID= t1.SubjectID and t2.country = t1.country and  t2.gene = t1.gene and t2.codon = t1.codon
              FOR XML PATH ('')
              )
             , 1, 1, '')
         ) ca (RefGenomeStr,TestGenomeStr)    
where nucleotide_order = 1
;

View schema
Execution time: 0,03 sec, rows selected: 5, rows affected: 15, absolute service time: 0,17 sec