Bigint unsigned value out of range

[András Keszthelyi]

Dear Experienced Forummates,

the problem simplified is this: given a table and I want to list the ID values and the next existing ID values and their difference (alias delta).

create table T1 ( ID serial, primary key (ID) ) engine=InnoDB;
insert into T1 values
(1),(2),(3),(5);

This query works as wanted:

select b.ID,
a.ID as NextID,
a.ID - b.ID as delta
from (select * from T1) as a,
(select * from T1) as b
where a.ID in (select min(ID)
from T1
where ID > b.ID
)
;

If I put it into a sub-query and append a where clause outside of the sub-query:

select *
from (select b.ID,
a.ID as NextID,
a.ID - b.ID as delta
from (select * from T1) as a,
(select * from T1) as b
where a.ID in (select min(ID)
from T1
where ID > b.ID
)
) as c
where delta > 1
;

it says that ERROR 1690 (22003): BIGINT UNSIGNED value is out of range. If I replace 'where delta > 1' with 'having delga > 1' then it also works.

The question is: Why? NextID, if exists, is at least one greater than ID...

Thx,
KEA.