Store select query's output in one array in postgres
Solution 1:
There are two ways. One is to aggregate:
SELECT array_agg(column_name::TEXT)
FROM information.schema.columns
WHERE table_name = 'aean'
The other is to use an array constructor:
SELECT ARRAY(
SELECT column_name
FROM information_schema.columns
WHERE table_name = 'aean'
)
I'm presuming this is for plpgsql. In that case you can assign it like this:
colnames := ARRAY(
SELECT column_name
FROM information_schema.columns
WHERE table_name='aean'
);
Solution 2:
I had exactly the same problem. Just one more working modification of the solution given by Denis (the type must be specified):
SELECT ARRAY(
SELECT column_name::text
FROM information_schema.columns
WHERE table_name='aean'
)
Solution 3:
CREATE OR REPLACE FUNCTION f_test_array(in _colname text)
returns text as $body$
DECLARE colnames text[];
begin
colnames := ARRAY(
SELECT column_name FROM information_schema.columns WHERE table_name='customer'
);
if exists(select _colname = any(colnames))
then return format('%s it exits.', _colname);
else return format('%s not exits.', _colname);
end if;
end
$body$
LANGUAGE plpgsql;
check if the column exists or not.
Key point: if exists(select _colname = any(colnames))
We can also using string_agg
String_agg usage:
CREATE OR REPLACE FUNCTION f_test_array1(in _colname text)
returns text as $body$
DECLARE colnames text;
begin
colnames := (SELECT string_agg(column_name,',') FROM information_schema.columns WHERE table_name='customer')::text;
if exists(select colnames ilike '%' || quote_literal(_colname) ||'%')
then return format('column %s exits.', _colname);
else return format('column %s does not exits.', _colname);
end if;
end
$body$
LANGUAGE plpgsql;
Solution 4:
Casting to the datatype "TEXT" will ensure that your queries will run without any problem. In plpgsql when we assign to a array variable, we need not use the type casting. My requirement was to get a CSV of all the column names of a particular table. I'd used the following code in plpgsql.
Declare col_list varchar[]:=NULL;
cols varchar:=NULL;
Begin
col_list := ARRAY(select t.name from frm_columns t where t.tname='emp_mstr');
cols := array_to_string(col_list,',');
return cols;
End;