Question

I have create a table using create table and with these column:

create table myschema.mytable(
    id serial PRIMARY KEY, 
    row_num integer, 
    col_num integer, 
    pix_centroid geometry, 
    pix_val double precision
)

When I am trying to populate it:

insert into pixelbased (id, row_num, col_num, pix_centroid, pix_val)
values (
    DEFAULT, 
    (select((ST_PixelAsPolygons(rast, 1)).x)  from mytable where rid=3),  
    (select((ST_PixelAsPolygons(rast, 1)).x)  from mytable where rid=3), 
    (select(ST_Centroid((ST_PixelAsPolygons(rast, 1)).geom)) from rwanda8 where rid=3),
    (select(ST_PixelAsPolygons(rast, 1)).val from mytable where rid=3)
) 

I am encountered with the following error:

ERROR: more than one row returned by a subquery used as an expression.

I know that since I have more than one row for every column it does make sense to have such an error. But I really need to have all the columns calculated as mentioned. Anyone knows what should I do?
In fact I want to insert the result the following query in the table:

select 
    (ST_PixelAsPolygons(rast, 1)).val as geomval1, 
    (ST_PixelAsPolygons(rast, 1)).x as X, 
    (ST_PixelAsPolygons(rast, 1)).y as Y, 
    (ST_Centroid((ST_PixelAsPolygons(rast, 1)).geom)) as geom 
from rwanda8 
where rid=3

Anyone knows what should I do?

Answer 1

Just use the select query in instead of the values

insert into pixelbased (row_num, col_num, pix_centroid, pix_val)
select
    (ST_PixelAsPolygons(rast, 1)).val as geomval1,
    (ST_PixelAsPolygons(rast, 1)).x as X,
    (ST_PixelAsPolygons(rast, 1)).y as Y,
    (ST_Centroid((ST_PixelAsPolygons(rast, 1)).geom)) as geom
from rwanda8 where rid=3

Do not insert the id as it is a serial and will generate itself.