Horton

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

Corey Huinker <corey.huinker@gmail.com>

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From: Corey Huinker <corey.huinker@gmail.com>
To: Isaac Morland <isaac.morland@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2023-03-28T20:23:26Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Make cast functions to type money error safe

  2. Make cast function from circle to polygon error safe

  3. Make geometry cast functions error safe

  4. Make cast functions from jsonb error safe

  5. Make many cast functions error safe

  6. Add SQL/JSON query functions

  7. Add soft error handling to some expression nodes

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

> On Mon, 19 Dec 2022 at 17:57, Corey Huinker <corey.huinker@gmail.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.