Creating a non-strict custom aggregate that initializes to the first value
| От | Timothy Garnett |
|---|---|
| Тема | Creating a non-strict custom aggregate that initializes to the first value |
| Дата | |
| Msg-id | CAPcyiQ2BuAc0438jbh5OnZDEgF=z4g8sdFbhLEy+MUpbqaxKWA@mail.gmail.com обсуждение исходный текст |
| Ответы |
Re: Creating a non-strict custom aggregate that initializes
to the first value
Re: Creating a non-strict custom aggregate that initializes to the first value |
| Список | pgsql-general |
Hi all,
I'm trying to create a custom aggregate function that returns the value from the first row (possibly null).
For ex.
Table t
a | b
-----
1 | A
2 | NULL
SELECT my_first(b order by a) => A
SELECT my_first(b order by a DESC) => NULL
The straightforward way would seem to be something like
CREATE OR REPLACE FUNCTION public.first_agg ( anyelement, anyelement )
RETURNS anyelement LANGUAGE sql IMMUTABLE STRICT AS $$
SELECT $1;
$$;
but if that is declared strict then it would take the first non-null value and return A in my second example, if declared non-strict then the initial state would be fed as null rather then the first value. Is there a way to declare the function non-strict (so that null values are passed) but still have it initialize to the first value like it would if it was strict?
Thanks for the help,
Tim
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