How can I extract the values from a record as individual columns in postgresql - postgresql

Question

How can I extract the values from a record as individual comuns in postgresql
SELECT
p.*,
(SELECT ROW(id,server_id,format,product_id) FROM products_images pi WHERE pi.product_id = p.id LIMIT 1) AS image
FROM products p
WHERE p.company = 1 ORDER BY id ASC LIMIT 10
Instead of
image
(3, 4, "jpeg", 7)
I would like to have
id | server_id | format | product_id
3 | 4 | jpeg | 7
Is there any way of selecting only one image for each product and return the columns directly instead of a record?

Answer 1

Try this:
create type xxx as (t varchar, y varchar, z int);
with a as
(
select row(table_name, column_name, (random() * 100)::int) x
from information_schema.columns
)
-- cannot cast directly to xxx, should cast to text first
select (x::text::xxx).t, (x::text::xxx).y, (x::text::xxx).z
from a
Alternatively, you can do this:
with a as
(
select row(table_name, column_name, (random() * 100)::int) x
from information_schema.columns
),
-- cannot cast directly to xxx, should cast to text first
b as (select x::text::xxx as w from a)
select
(w).t, (w).y, (w).z
from b
To select all fields:
with a as
(
select row(table_name, column_name, (random() * 100)::int) x
from information_schema.columns
),
-- cannot cast directly to xxx, should cast to text first
b as (select x::text::xxx as w from a)
select
(w).*
from b
You can do this too, but this makes the whole exercise of using ROW a pointless one when you can just remove the ROW function and re-pick it up from outside of cte/derived table. I surmised the OP's ROW came from a function; for which he should use the codes above, not the following:
with a as
(
select row(table_name, column_name, (random() * 100)::int)::xxx x
from information_schema.columns
)
select
(x).t, (x).y, (x).z
from a

Answer 2

Just specify the components of your struct:
SELECT a,b,c,(image).id, (image).server_id, ...
FROM (
SELECT
p.*,
(SELECT ROW(id,server_id,format,product_id) FROM products_images pi WHERE pi.product_id = p.id LIMIT 1) AS image
FROM products p
WHERE p.company = 1 ORDER BY id ASC LIMIT 10
) as subquery
But anyway, I would rework the query and use a join instead of a subclause.
SELECT DISTINCT ON (p.*) p.*,
p.id,pi.server_id,pi.format,pi.product_id
FROM products p
LEFT JOIN product_images pi ON pi.product_id = p.id
WHERE p.company = 1
ORDER BY id ASC
LIMIT 10
But I believe you have to specify all the p-fields in the distinct separately to ensure just one image is loaded per product.

Answer 3

Try this, will work on your existing code with minimal modification(if creating a type is a minimal modification for you ;-)
create type image_type as (id int, server_id int, format varchar, product_id int);
SELECT
p.*,
( (SELECT ROW(id,server_id,format,product_id)
FROM products_images pi
WHERE pi.product_id = p.id LIMIT 1)::text::image_type ).*
FROM products p
WHERE p.company = 1 ORDER BY id ASC LIMIT 10
Proof-of-concept code:
Create type first:
create type your_type_here as (table_name varchar, column_name varchar)
Actual code:
select
a.b,
( (select row(table_name, column_name)
from information_schema.columns limit 1)::text::your_type_here ).*
from generate_series(1,10) as a(b)
But I guess you should tackle it with GROUP BY' andMAXcombo or useDISTINCT ON` like what Daniel have posted

Answer 4

every table has an associated composite type of the same name
https://www.postgresql.org/docs/current/plpgsql-declarations.html#PLPGSQL-DECLARATION-ROWTYPES
So, this code
drop table if exists "#typedef_image"
;
create temp table "#typedef_image"(
id int,
server_id int,
format text,
product_id int
)
;
select (row(3, 4, 'jpeg', 7)::"#typedef_image").*
will work