Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions
| От | Corey Huinker |
|---|---|
| Тема | Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions |
| Дата | |
| Msg-id | CADkLM=eD_S8mGhPfu5+hXXvXgR0-cxGpGd9dgPzD+nCuO7HFaQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: CAST(... ON DEFAULT) - WIP build on top of Error-Safe User Functions (Isaac Morland <isaac.morland@gmail.com>) |
| Список | pgsql-hackers |
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.
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