I\'m trying to aggregate a \'STRING\' field in SQLServer. I would like to find the same function LISTAGG like in Oracle .
Do you know how to do the same function or
Starting in SQL Server 2017 the STRING_AGG function is available which simplifies the logic considerably:
select FieldA, string_agg(FieldB, '') as data
from yourtable
group by FieldA
See SQL Fiddle with Demo
In SQL Server you can use FOR XML PATH to get the result:
select distinct t1.FieldA,
  STUFF((SELECT distinct '' + t2.FieldB
         from yourtable t2
         where t1.FieldA = t2.FieldA
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,0,'') data
from yourtable t1;
See SQL Fiddle with Demo