Turning a subselect into an array

[Jim C. Nasby]

I'm sure this has been answered before, but the search seems to be down
again.

How can I convert the results of a subselect into an array? IE:

CREATE TABLE a(a int, b int, c int[]);
INSERT INTO table_a
SELECT a, b, (SELECT c FROM table_c WHERE table_c.parent = table_b.id)
FROM table_b
;
--
Jim C. Nasby, Database Consultant decibel@decibel .org
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[Michael Fuhr]

Re: Turning a subselect into an array

On Thu, Oct 28, 2004 at 05:37:29PM -0500, Jim C. Nasby wrote:[color=blue]
> I'm sure this has been answered before, but the search seems to be down
> again.
>
> How can I convert the results of a subselect into an array? IE:
>
> CREATE TABLE a(a int, b int, c int[]);
> INSERT INTO table_a
> SELECT a, b, (SELECT c FROM table_c WHERE table_c.parent = table_b.id)
> FROM table_b[/color]

See the "Array Constructors" section in the PostgreSQL documentation:

http://www.postgresql.org/docs/7.4/static/sql-expressions.html#SQL-SYNTAX-ARRAY-CONSTRUCTORS

INSERT INTO table_a
SELECT a, b, ARRAY(SELECT c FROM table_c WHERE table_c.parent = table_b.id)
FROM table_b

--
Michael Fuhr

http://www.fuhr.org/~mfuhr/

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[Jim C. Nasby]

Re: Turning a subselect into an array

Ok, next stupid question that I can't find in the docs... How would I
join a table to an array? IE: if I have an array of primary keys for
some table and I want to get the name field from that table and turn it
back into an array, how would I do that?

On Thu, Oct 28, 2004 at 05:21:52PM -0600, Michael Fuhr wrote:[color=blue]
> On Thu, Oct 28, 2004 at 05:37:29PM -0500, Jim C. Nasby wrote:[color=green]
> > I'm sure this has been answered before, but the search seems to be down
> > again.
> >
> > How can I convert the results of a subselect into an array? IE:
> >
> > CREATE TABLE a(a int, b int, c int[]);
> > INSERT INTO table_a
> > SELECT a, b, (SELECT c FROM table_c WHERE table_c.parent = table_b.id)
> > FROM table_b[/color]
>
> See the "Array Constructors" section in the PostgreSQL documentation:
>
> http://www.postgresql.org/docs/7.4/s...Y-CONSTRUCTORS
>
> INSERT INTO table_a
> SELECT a, b, ARRAY(SELECT c FROM table_c WHERE table_c.parent = table_b.id)
> FROM table_b
>
> --
> Michael Fuhr
> http://www.fuhr.org/~mfuhr/
>
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>[/color]

--
Jim C. Nasby, Database Consultant decibel@decibel .org
Give your computer some brain candy! www.distributed.net Team #1828

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[Michael Fuhr]

Re: Turning a subselect into an array

On Fri, Oct 29, 2004 at 05:13:02PM -0500, Jim C. Nasby wrote:[color=blue]
> Ok, next stupid question that I can't find in the docs... How would I
> join a table to an array? IE: if I have an array of primary keys for
> some table and I want to get the name field from that table and turn it
> back into an array, how would I do that?[/color]

See the "Subquery Expressions" and "Row and Array Comparisons"
sections in the PostgreSQL documentation:

http://www.postgresql.org/docs/7.4/static/functions-subquery.html

http://www.postgresql.org/docs/7.4/static/functions-comparisons.html

If I understand you correctly, this should work:

SELECT ARRAY(SELECT name FROM foo WHERE id = ANY(ARRAY[1,2,3]));

A test I just ran showed "id = ANY(ARRAY[1,2,3])" doing a sequential
scan whereas "id IN (1,2,3)" did an index scan, so you might want to
use the latter if possible.

--
Michael Fuhr

http://www.fuhr.org/~mfuhr/

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