Re: looking for an array-extract-item-as-it operator
| От | Peter Krauss |
|---|---|
| Тема | Re: looking for an array-extract-item-as-it operator |
| Дата | |
| Msg-id | CAHEREtsLvKUbOppq4vsdL6+3gKzQaugP9KRbokATe6=DosUG5w@mail.gmail.com обсуждение исходный текст |
| Ответ на | looking for an array-extract-item-as-it operator (Peter Krauss <ppkrauss@gmail.com>) |
| Список | pgsql-hackers |
(ops, sending to the pgsql-hackers, see the complete thread below)
Adding a formal suggestion after discussion: to include a fast array_getarray() function!
CREATE FUNCTION array_getarray( m anyarray, idx int ) RETURNS anyarray AS $f$
-- this is a slow workaround for an (need for) internal operation
WITH item AS (SELECT unnest($1[$2:$2]) as x)
SELECT array_agg(x) FROM item;
$f$ LANGUAGE sql IMMUTABLE;
-- EXAMPLE:
SELECT array_getarray(zz,2) as x, zz[2:2] as y -- x is not same as y!
FROM ( SELECT '{{1,2},{33,44}}'::int[][] as zz ) as tt
2016-01-07 7:26 GMT-02:00 Peter Krauss <ppkrauss@gmail.com>:
2016-01-06 20:50 GMT-02:00 Tom Lane <tgl@sss.pgh.pa.us>:Peter Krauss <ppkrauss@gmail.com> writes:
> I need to access an array-item from an array of arrays.
Multi-dimensional arrays in Postgres are not "arrays of arrays".Thanks, you expressed in a little phrase something fundamental to think about pg-arrays (!), the pg-Guide need some notices like yours, to remember people like me ;-) Well... The good answer closes the question.- - - -We can imagine that the "multidimensional array world" is like a data type, that is distinct from the "usual array" data type...I am starting other discussion...Let me explain how the question arrives for me: was after working with JSONB, where arrays are of "usual array" type.Now that PostgreSQL 9.4+ incorporated definitely JSONB, the SQL array data type is an important "intermediate" between JSONB and usual SQL structures (and type operation algebras).So, perhaps, PostgreSQL 9.4+ will need a kind of "usual array type", a new internal type, and a cast function: with this new type will be possible to simplify the work with JSONB, and do other things like array_agg(array[x,y]).... It is not for final user, perhaps only for developers, or library plugins: an "intermediate" type that not broken compatibility... Not very useful, a type only to formally express things like to eficient cast, etc.
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