with TABLE_A as
(
    select 'A' as COL1 from dual     union all
     select 'B' from dual    union all
     select 'C' from dual
), TABLE_B as
(
    select 'A1' as col2 from dual union all
     select 'A2' from dual union all
     select 'A3' from dual union all
     select 'B2' from dual union all
     select 'B1' from dual union all
     select 'C1' from dual
) 
select 
    ta.col1,
     (select max(col2) from table_b tb where tb.col2 like ta.col1 || '%') as col2
from 
    table_a ta;