Thread: Turning a subselect into an array
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
Give your computer some brain candy! www.distributed.net Team #1828
Windows: "Where do you want to go today?"
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On Thu, Oct 28, 2004 at 05:37:29PM -0500, Jim C. Nasby wrote: > 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 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/
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: > On Thu, Oct 28, 2004 at 05:37:29PM -0500, Jim C. Nasby wrote: > > 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 > > 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/ > > ---------------------------(end of broadcast)--------------------------- > TIP 7: don't forget to increase your free space map settings > -- Jim C. Nasby, Database Consultant decibel@decibel.org Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"
On Fri, Oct 29, 2004 at 05:13:02PM -0500, Jim C. Nasby wrote: > 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? 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/
Thanks again for the help. I did manage to find that after a bunch of searching in the mailing list. There should really be a portion of the docs dedicated to array handling. On Fri, Oct 29, 2004 at 10:40:57PM -0600, Michael Fuhr wrote: > On Fri, Oct 29, 2004 at 05:13:02PM -0500, Jim C. Nasby wrote: > > 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? > > 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/ > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) > -- Jim C. Nasby, Database Consultant decibel@decibel.org Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"