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From: Corey Huinker <[email protected]>
To: Isaac Morland <[email protected]>
Cc: [email protected]
Subject: Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions
Date: Tue, 28 Mar 2023 16:23:26 -0400
Message-ID: <CADkLM=eD_S8mGhPfu5+hXXvXgR0-cxGpGd9dgPzD+nCuO7HFaQ@mail.gmail.com> (raw)
In-Reply-To: <CAMsGm5dpfm2PHL8XZvC-JSd+UPkgx3rpReUA=G=4+rUCH+Ntcw@mail.gmail.com>
References: <CADkLM=fv1JfY4Ufa-jcwwNbjQixNViskQ8jZu3Tz_p656i_4hQ@mail.gmail.com>
	<CAMsGm5dpfm2PHL8XZvC-JSd+UPkgx3rpReUA=G=4+rUCH+Ntcw@mail.gmail.com>

On Tue, Mar 28, 2023 at 3:25 PM Isaac Morland <[email protected]>
wrote:

> On Mon, 19 Dec 2022 at 17:57, Corey Huinker <[email protected]>
> 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.

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