Mysql table column update issue
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I am using below query to update a column but not able to update.

update table1
 set month_0val = (select v1.sumvalue 
 from ( select r1.reg_id, sum(backbook.bal) as sumvalue
 from  table2 backbook , table3 s , table4 r1
 where month(backbook.Date_AsOf) = month(s.MONTH_AS_OF - INTERVAL 12 MONTH) and year(backbook.Date_AsOf) =  year(s.MONTH_AS_OF - INTERVAL 12 MONTH)  and  backbook.a_region_id = r1.region_code
 and r1.org_id = org_id and  backbook.A_ProdType_Code != 25  and s.SC_ID = sc_id group by backbook.A_Region_ID ) v1
 where v1.reg_id = table1.Region);

even the inner query returns result.

Please help.