Обсуждение: how can I select into an array?

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how can I select into an array?

От
"Andy Kriger"
Дата:

I would like to select strings from a table and return them as an array
For example,
select new_array(name) from my_tbl
would return
String[] { name1, name2, name3, etc }

Is this possible with built-in SQL/psql functions?
If not, how hard would it be to write a function that does this? (given that I have coding experience but none writing pgsql functions)

Andy Kriger | Software Mechanic | Greater Than One, Inc.
28 West 27th Street | 7th Floor | New York, NY 10001
P: 212.252.7197 | F: 212.252.7364 | E: akriger@greaterthanone.com

Re: how can I select into an array?

От
Pavel Stehule
Дата:
hello,

try:

CREATE OR REPLACE FUNCTION aggregate_array(ANYARRAY,ANYELEMENT) RETURNS
ANYARRAY AS '
   SELECT
    CASE
     WHEN $1 IS NULL
     THEN ARRAY[$2]
     WHEN $2 IS NULL
     THEN $1
     ELSE array_append($1,$2)
 END;
' LANGUAGE 'SQL';

CREATE AGGREGATE aggarray (BASETYPE = ANYELEMENT, SFUNC = aggregate_array,
STYPE = ANYARRAY);

or

CREATE AGGREGATE aggarray (basetype = anyelement, sfunc = array_append,
stype = anyarray, initcond = '{}' );

testdb011=> SELECT count(*), aggarray(prijmeni) FROM lide GROUP BY
prijmeni ~ '.*á';

regards
Pavel Stehule




On Fri, 6 Feb 2004, Andy Kriger wrote:

> I would like to select strings from a table and return them as an array
> For example,
> select new_array(name) from my_tbl
> would return
> String[] { name1, name2, name3, etc }
>
> Is this possible with built-in SQL/psql functions?
> If not, how hard would it be to write a function that does this? (given that
> I have coding experience but none writing pgsql functions)
>
> Andy Kriger | Software Mechanic | Greater Than One, Inc.
> 28 West 27th Street | 7th Floor | New York, NY 10001
> P: 212.252.7197 | F: 212.252.7364 | E: akriger@greaterthanone.com
>
>

Re: how can I select into an array?

От
"Andy Kriger"
Дата:
Thank you for your response - I should have mention I'm using Postgres 7.2.x
ANYARRAY does not appear to exist in that version
Is there a workaround?

-----Original Message-----
From: Pavel Stehule [mailto:stehule@kix.fsv.cvut.cz]
Sent: Friday, February 06, 2004 10:49 AM
To: Andy Kriger
Cc: Pgsql-General
Subject: Re: [GENERAL] how can I select into an array?

hello,

try:

CREATE OR REPLACE FUNCTION aggregate_array(ANYARRAY,ANYELEMENT) RETURNS
ANYARRAY AS '
   SELECT
    CASE
     WHEN $1 IS NULL
     THEN ARRAY[$2]
     WHEN $2 IS NULL
     THEN $1
     ELSE array_append($1,$2)
 END;
' LANGUAGE 'SQL';

CREATE AGGREGATE aggarray (BASETYPE = ANYELEMENT, SFUNC = aggregate_array,
STYPE = ANYARRAY);

or

CREATE AGGREGATE aggarray (basetype = anyelement, sfunc = array_append,
stype = anyarray, initcond = '{}' );

testdb011=> SELECT count(*), aggarray(prijmeni) FROM lide GROUP BY prijmeni
~ '.*á';

regards
Pavel Stehule




On Fri, 6 Feb 2004, Andy Kriger wrote:

> I would like to select strings from a table and return them as an
> array For example, select new_array(name) from my_tbl would return
> String[] { name1, name2, name3, etc }
>
> Is this possible with built-in SQL/psql functions?
> If not, how hard would it be to write a function that does this?
> (given that I have coding experience but none writing pgsql functions)
>
> Andy Kriger | Software Mechanic | Greater Than One, Inc.
> 28 West 27th Street | 7th Floor | New York, NY 10001
> P: 212.252.7197 | F: 212.252.7364 | E: akriger@greaterthanone.com
>
>

Re: how can I select into an array?

От
Pavel Stehule
Дата:
if you can in plpgsql 7.2.x return array of known type, you can replace
anyarray and anyelement like varchar[], varchar. But I don't know if it
7.2 supported.

Pavel

On Fri, 6 Feb 2004, Andy Kriger wrote:

> Thank you for your response - I should have mention I'm using Postgres 7.2.x
> ANYARRAY does not appear to exist in that version
> Is there a workaround?
>
> -----Original Message-----
> From: Pavel Stehule [mailto:stehule@kix.fsv.cvut.cz]
> Sent: Friday, February 06, 2004 10:49 AM
> To: Andy Kriger
> Cc: Pgsql-General
> Subject: Re: [GENERAL] how can I select into an array?
>
> hello,
>
> try:
>
> CREATE OR REPLACE FUNCTION aggregate_array(ANYARRAY,ANYELEMENT) RETURNS
> ANYARRAY AS '
>    SELECT
>     CASE
>      WHEN $1 IS NULL
>      THEN ARRAY[$2]
>      WHEN $2 IS NULL
>      THEN $1
>      ELSE array_append($1,$2)
>  END;
> ' LANGUAGE 'SQL';
>
> CREATE AGGREGATE aggarray (BASETYPE = ANYELEMENT, SFUNC = aggregate_array,
> STYPE = ANYARRAY);
>
> or
>
> CREATE AGGREGATE aggarray (basetype = anyelement, sfunc = array_append,
> stype = anyarray, initcond = '{}' );
>
> testdb011=> SELECT count(*), aggarray(prijmeni) FROM lide GROUP BY prijmeni
> ~ '.*á';
>
> regards
> Pavel Stehule
>
>
>
>
> On Fri, 6 Feb 2004, Andy Kriger wrote:
>
> > I would like to select strings from a table and return them as an
> > array For example, select new_array(name) from my_tbl would return
> > String[] { name1, name2, name3, etc }
> >
> > Is this possible with built-in SQL/psql functions?
> > If not, how hard would it be to write a function that does this?
> > (given that I have coding experience but none writing pgsql functions)
> >
> > Andy Kriger | Software Mechanic | Greater Than One, Inc.
> > 28 West 27th Street | 7th Floor | New York, NY 10001
> > P: 212.252.7197 | F: 212.252.7364 | E: akriger@greaterthanone.com
> >
> >
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster
>

Re: how can I select into an array?

От
Tom Lane
Дата:
"Andy Kriger" <akriger@greaterthanone.com> writes:
> I would like to select strings from a table and return them as an array

You can do that beginning in 7.4 with the ARRAY(sub-select) construct.

regression=# select f1 from text_tbl;
        f1
-------------------
 doh!
 hi de ho neighbor
(2 rows)

regression=# select array(select f1 from text_tbl);
          ?column?
----------------------------
 {doh!,"hi de ho neighbor"}
(1 row)

regression=#

In prior versions you could probably fake it with a loop in a plpgsql
function, but it'd be kinda awkward.

            regards, tom lane

Re: how can I select into an array?

От
Joe Conway
Дата:
Pavel Stehule wrote:

> CREATE AGGREGATE aggarray (BASETYPE = ANYELEMENT, SFUNC = aggregate_array,
> STYPE = ANYARRAY);

Or, from the docs, see:
http://www.postgresql.org/docs/current/static/xaggr.html

CREATE AGGREGATE array_accum (
      sfunc = array_append,
      basetype = anyelement,
      stype = anyarray,
      initcond = '{}'
);

array_append() is built-in in 7.4 -- and note both Pavel's solution and
this one require 7.4.x

HTH,

Joe

Re: how can I select into an array?

От
Joe Conway
Дата:
Pavel Stehule wrote:
> if you can in plpgsql 7.2.x return array of known type, you can replace
> anyarray and anyelement like varchar[], varchar. But I don't know if it
> 7.2 supported.

PL/pgSQL array support in anything earlier than 7.4 is pretty weak. I
would strongly recommend upgrading to 7.4 if arrays are important to you.

Joe

Re: how can I select into an array?

От
"Andy Kriger"
Дата:
this is a followup to my original message for anyone else stuck on older psql versions...
 
i wrote a function to accomplish selecting into an array which works in 7.2.1
you will need to 'createlang plpgsql' (see the docs on procedural languages) before you can use it
it takes a SQL query as an arg and returns an array aggregated from the result column named 'arrayval'
it is written to work with varchars but could easily be modified to work with other data types
 
-- create an array from the results of a query
-- query must return a column named arrayval
-- $1 = query string
CREATE OR REPLACE FUNCTION array_query(VARCHAR)
RETURNS VARCHAR[]
AS '
DECLARE
    query ALIAS FOR $1;
    rec RECORD;
    str VARCHAR;
    arr VARCHAR[];
BEGIN
    str := ''{'';
    FOR rec IN EXECUTE query LOOP  
        str := str || ''"'' || rec.arrayval || ''"'' || '','';
    END LOOP;
    str := str || ''}'';
    SELECT INTO arr str;
    RETURN arr;
END;
' LANGUAGE 'plpgsql';

From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org] On Behalf Of Andy Kriger
Sent: Friday, February 06, 2004 10:37 AM
To: Pgsql-General
Subject: [GENERAL] how can I select into an array?

I would like to select strings from a table and return them as an array
For example,
select new_array(name) from my_tbl
would return
String[] { name1, name2, name3, etc }

Is this possible with built-in SQL/psql functions?
If not, how hard would it be to write a function that does this? (given that I have coding experience but none writing pgsql functions)

Andy Kriger | Software Mechanic | Greater Than One, Inc.
28 West 27th Street | 7th Floor | New York, NY 10001
P: 212.252.7197 | F: 212.252.7364 | E: akriger@greaterthanone.com

Re: how can I select into an array?

От
elein
Дата:
On Fri, Feb 06, 2004 at 12:08:16PM -0500, Tom Lane wrote:
> "Andy Kriger" <akriger@greaterthanone.com> writes:
> > I would like to select strings from a table and return them as an array
>
> You can do that beginning in 7.4 with the ARRAY(sub-select) construct.
>
> regression=# select f1 from text_tbl;
>         f1
> -------------------
>  doh!
>  hi de ho neighbor
> (2 rows)
>
> regression=# select array(select f1 from text_tbl);
>           ?column?
> ----------------------------
>  {doh!,"hi de ho neighbor"}
> (1 row)
>
> regression=#
>
> In prior versions you could probably fake it with a loop in a plpgsql
> function, but it'd be kinda awkward.
>
>             regards, tom lane
>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend

Joe Conway supplied a 7.3 version of function that
could help you do this.  I have not tested it in
7.2, however.  The details of this function for
getting the next array index for appending to the
array are written up in http://www.varlena.com/GeneralBits/24.html

 CREATE OR REPLACE FUNCTION array_next(text[]) returns int AS '
   DECLARE
      arr alias for $1;
      high int;
      BEGIN
         high := 1 +
            replace(split_part(array_dims(arr),'':'',2),'']'','''')::int;
         RETURN high;
      END;
   ' LANGUAGE 'plpgsql' IMMUTABLE STRICT;

   create table mytable (myarray text[]);
   insert into mytable values ('{"abc","d e f"}');
   update mytable set myarray[array_next(myarray)] = 'new element';
   regression=# select * from mytable;
               myarray
   -----------------------------
      {abc,"d e f","new element"}
   (1 row)

Elein

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