Equivalent of Select #variable in Spring Data Jpa - spring

Question

I need to run a long query on a spring data jpa method call.
What is the equivalent of Select #sql in spring jpa.
I am getting exception when i try to execute it as a native query.
Below is the query that is working fine in SQL server
Declare #sql varchar(max) = 'select '
select #sql = #sql + 'sum(' + c.name + ')' + ' AS ' + c.name + ','
from sys.columns c
inner join sys.tables t on c.object_id = t.object_id
inner join sys.types ty on
c.user_type_id = ty.user_type_id
where
ty.name in ('bigint') and
t.name = 'my_used_features'
select #sql = LEFT(#sql,LEN(#sql)-1) + ' from my_used_features '
EXEC (#sql)
I want to write the same query as native query in my repository class.But I am getting exception like ....... EXEC (#sql)> starts a quoted range at 342, but never ends it.I am not able to figure out the issue.Can anyone please help me on what am I doing wrong.
#Query
(value="Declare #sql varchar(max) = 'select '\r\n"
+ " \r\n"
+ " select #sql = #sql + 'sum(' + c.name + ')' + ' AS ' + c.name + ',' \r\n"
+ " from sys.columns c\r\n"
+ " inner join sys.tables t on c.object_id = t.object_id\r\n"
+ " inner join sys.types ty on\r\n"
+ " c.user_type_id = ty.user_type_id\r\n"
+ " where\r\n"
+ " ty.name in ('bigint') and\r\n"
+ " t.name = 'my_used_features'\r\n"
+ " \r\n"
+ " select #sql = LEFT(#sql,LEN(#sql)-1) + ' from my_used_features ' \r\n"
+ " \r\n"
+ " EXEC (#sql)",nativeQuery=true)
Map<String,Integer> findSum();