[tarantool-patches] Re: [PATCH 6/6] sql: allow to specify UNSIGNED column type

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

On 18/07/2019 22:56, n.pettik wrote:
> 
> 
>> On 18 Jul 2019, at 23:18, Vladislav Shpilevoy <v.shpilevoy@tarantool.org <mailto:v.shpilevoy@tarantool.org>> wrote:
>>
>> Hi!
>>
>> Thanks for the fixes!
>>
>>>> -------------------------
>>>> vdbe.c:307
>>>>
>>>>> case FIELD_TYPE_INTEGER:
>>>>> case FIELD_TYPE_UNSIGNED:
>>>>> if ((record->flags & MEM_Int) == MEM_Int)
>>>>> return 0;
>>>>> if ((record->flags & MEM_UInt) == MEM_UInt)
>>>>> return 0;
>>>>> if ((record->flags & MEM_Real) == MEM_Real) {
>>>>> int64_t i = (int64_t) record->u.r;
>>>>> if (i == record->u.r)
>>>>> mem_set_int(record, record->u.r,
>>>>>     record->u.r <= -1);
>>>>> return 0;
>>>>> }
>>>>
>>>> It is a part of function mem_apply_type. When target type is
>>>> UNSIGNED, and a value is MEM_Int, you do nothing. Why? Looks like
>>>> it is possible to pass here a negative value, and CAST UNSIGNED
>>>> would do nothing.
>>>
>>> Basically, this function implements sort of implicit cast
>>> which takes place before comparison/assignment.
>>> For comparisons it makes no sense - we can compare
>>> integer with unsigned value - the latter is always greater.
>>> For assignment it is also meaningless: if we attempt
>>> at inserting negative values to unsigned field appropriate
>>> error will be raised anyway. If you can come up with
>>> specific example, let’s discuss it.
>>>
>>
>> I can't provide a test. But the function is named mem_apply_type,
>> and it doesn't apply type, when it is unsigned, and a value is
>> negative. Doesn't it look wrong to you?
>>
>> If some code wants to get an integer, it can apply FIELD_TYPE_INTEGER
>> instead of FIELD_TYPE_UNSIGNED. IMO, an attempt to apply unsigned
>> to int should raise an error here. Otherwise this function can't
>> be named 'apply_type' because it ignores negative -> unsigned case.
> 
> Okay, let’s rename it. I can suggest these options:
> 
> mem_cast_implicit()
> mem_cast_implicit_to_type()
> mem_implicit_cast_to_type()
> mem_convert_implicit()
> mem_convert_to_type()
> mem_type_coerce_implicit()
> mem_type_implicit_coercion()
> mem_type_coercion_implicit()
> mem_implicit_type_juggling()
> mem_implicit_juggle_to_type()
> mem_do_implicit_conversion()
> mem_do_implicit_coercion()
> 
> Or any other combination :)
> 

But it is not implicit. It just does not work, when a value is negative,
and type is unsigned.