Re: [Firebird-devel] Adding NOT NULL fields with DEFAULT

[Vlad K. <hv...@us...>]

> Vlad Khorsun wrote:
>>> Ann W. Harrison wrote:
>>>> Here's the problem I see, and it may exist already.
>>>>
>>>> Create a table, which creates format 1 for that table.
>>>> Store a bunch of records.
>>>>
>>>> Add a NOT NULL field with a default value of 'ABC',
>>>> which creates format 2 for the table.  The new format
>>>> includes the default value.
>>>>
>>>> Now if you read records for that table, the new field's
>>>> value is 'ABC'.
>>>>
>>> That's ok.
>>>
>>>> Now alter the table, changing the default value to '123',
>>>> creating a new format 3 which includes the new default
>>>> for that field.
>>>>
>>>> Read the same records again and the value is probably going
>>>> to be '123'.
>>>>
>>> If the record format is 2, it should return 'ABC'. If the record is updated and written in the 
>>> format 3, 'ABC' should be written to the field so it doesn't catch the format 3 value when 
>>> reading it.
>> 
>>     What if record still stored in format 1 ?
>> 
> Records at format 1 (which does not have the field added in 2) should use the default value stored in format 2. 
> So 'ABC' should be written when updating to format 3 too.

    We have record, stored in format 1, without additional field. We have formats 2 and 3
with different default values for the same field. When engine read record it converts it into
most current format - format 3 in this case. The question is - what value should be in new
field, added with format 2 ? 'ABC' or '123' ? I think - 'ABC'.

Regards,
Vlad