Hi All,
On Tue, 10 Feb 2009, Przemyslaw Czerpak wrote:
> We have to define also supported math operations and item type for results.
> I suggest to make it date compatible too and define that date + timestamp
> and timestamp + date gives timestamp as result. The list of legal operations
> will look like:
> <t> + <t> => <t>
> <t> - <t> => <n>
> <t> + <n> => <t>
> <n> + <t> => <t>
> <t> - <n> => <t>
>
> <d> + <t> => <t>
> <t> + <d> => <t>
> <d> - <t> => <n>
> <t> - <d> => <n>
We also have to define relation operators behavior: ==, =, <, >, <=, >=
when DATE and TIMESTAMP are used.
We have the following choices:
1. compare only date part ignoring the time with the exception for ==
operator which will make exact comparison. For this exact comparision
we also have two choices:
a. strict type checking => results always .F.
b. if dates are equal and time part in TIMESTAMP item is 0 then
result is .T. otherwise .F.
2. convert DATE to TIMESTAMP setting 00:00 as TIME and compare items
like two TIMESTAMP values.
In such way works xHarbour.
3. use asymmetric comparison like for strings so:
FIELD->DATETIME <= date()
will work but
date() => FIELD->DATETIME
won't.
Now my opinion:
I do not like 3-rd version because it may be too complicated for users
and normal usage.
2-nd one has some bad side effect. User cannot use DATE in filter
expressions like:
FIELD->DATETIME <= date()
because date() value after conversion will have time part set to 0
so it will be smaller then TIMESTAMP value calculated today (except
the midnight).
For me the best choice is 1.
Probably 1b but I also found 1a as usable in some cases. The question
is how deeply we want to hide difference between DATE and TIMESTAMP
types. If it should be fully hidden like for numbers (we do not make
any difference between HB_IT_INTEGER, HB_IT_LONG and HB_IT_DOUBLE in
== comparision) then we should chose 1b.
I would like to hear your opinions.
best regards,
Przemek
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