mysql - Unselected value from a group by query to subquery

Question

I have to provide an unselected set of values from a group by query to a subquery

Like

col_1	col_2	col_3
1	a	154
2	a	845
3	b	558
4	c	88

Answer 1

Your approach is wrong simply join the tables and aggregate the values

select col2,sum(balance) 
from tb_1
join accounts a on a.id = tb_1.col3
group by col2;