Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions

On Tue, Mar 28, 2023 at 3:25 PM Isaac Morland <isaac(dot)morland(at)gmail(dot)com>
wrote:

> On Mon, 19 Dec 2022 at 17:57, Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
> wrote:
>
>>
>> Attached is my work in progress to implement the changes to the CAST()
>> function as proposed by Vik Fearing.
>>
>> CAST(expr AS typename NULL ON ERROR)
>> will use error-safe functions to do the cast of expr, and will return
>> NULL if the cast fails.
>>
>> CAST(expr AS typename DEFAULT expr2 ON ERROR)
>> will use error-safe functions to do the cast of expr, and will return
>> expr2 if the cast fails.
>>
>
> Is there any difference between NULL and DEFAULT NULL?
>

What I think you're asking is: is there a difference between these two
statements:

SELECT CAST(my_string AS integer NULL ON ERROR) FROM my_table;

SELECT CAST(my_string AS integer DEFAULT NULL ON ERROR) FROM my_table;

And as I understand it, the answer would be no, there is no practical
difference. The first case is just a convenient shorthand, whereas the
second case tees you up for a potentially complex expression. Before you
ask, I believe the ON ERROR syntax could be made optional. As I implemented
it, both cases create a default expression which then typecast to integer,
and in both cases that expression would be a const-null, so the optimizer
steps would very quickly collapse those steps into a plain old constant.