Oracle 21c

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create table t (a number(10, 4), b number(10, 4));
insert into t (a, b) values (105, 100);
1 rows affected

insert into t (a, b) values (115, 134);
1 rows affected

insert into t (a, b) values (120, 110);
1 rows affected

insert into t (a, b) values (140, 170);
1 rows affected

insert into t (a, b) values (140, 190);
1 rows affected

select t.*, 
  case when abs(b / a - 1.0) < 0.06 then '0-6%'
       when abs(b / a - 1.0) < 0.15 then '6-15%'
       when abs(b / a - 1.0) < 0.20 then '15-20%'
       else '20%+' end as segment       
from t


A
B
SEGMENT


105
100
0-6%

115
134
15-20%

120
110
6-15%

140
170
20%+

140
190
20%+