select lower and upper from lower only table - mysql

Question

How can I transform a normalized table with family, name and 'lowerbound' number to a result set with family, name, lower and upper bound, where upper bound is defined as min(lowerbound of family) > current lowerbound and if no number like this exists, use a provided number
for example, if this is the schema and data:
create table records(
family varchar(10),
name varchar(10),
lowbound int(4)
);
insert into records
values
('letters', 'a',1),('letters', 'b',3),('letters', 'c',3),('letters', 'd',3),
('letters', 'e',7),('letters', 'f',7),('numbers', '12',1), ('numbers', '15',1), ('numbers', '18',4);
and the provided number is 9, then the result set should be:
| FAMILY | NAME | LOWER | UPPER |
|---------|------|-------|-------|
| letters | a | 1 | 3 |
| letters | b | 3 | 7 |
| letters | c | 3 | 7 |
| letters | d | 3 | 7 |
| letters | e | 7 | 9 |
| letters | f | 7 | 9 |
| numbers | 12 | 1 | 4 |
| numbers | 15 | 1 | 4 |
| numbers | 18 | 4 | 9 |

Answer 1

Try this out:
SELECT r1.family, r1.name, r1.lowbound lower, coalesce(min(r2.lowbound), 9) upper
FROM records r1
LEFT JOIN records r2 ON r1.family = r2.family AND r1.lowbound < r2.lowbound
GROUP BY r1.family, r1.name, r1.lowbound
Fiddle here

Answer 2

I think the easiest way to express this is with a correlated subquery in the select clause:
select r.*,
coalesce((select r2.lowbound
from records r2
where r2.family = r.family and
r2.lowbound > r.lowbound
order by r2.lowbound
limit 1
), 9) as highbound
from records r;
The coalesce() handles the case where there is no value. In that case, your substitution value of 9 is used.
Here is the SQL Fiddle.