select 
PDBC_PFX, BSBS_TYPE, 
STRING_AGG(CAST(BSTX_TEXT as VARCHAR(MAX)), '') WITHIN GROUP ( ORDER BY BSTX_SEQ_NO ASC ) as BSTX0
from dbo.CMC_BSTX_SUM_TEXT
where PDBC_PFX = 'EH38' and BSBS_TYPE = 'SOBD'
GROUP BY PDBC_PFX, BSBS_TYPE