Count for each columns in table (not null) PostgreSQL PL/pgSQL - postgresql

Question

I am trying to count the number of rows that do not contain null for each column in the table
There is a simple table actor_new
The first 2 columns (actor_id, first_name) contain 203 rows not null
Other 2 columns (last_name, last_update) contain 200 rows not null
This is a simple test that outputs the same value for all columns, but if you perform select separately, then everything works correctly, please help me understand the LOOP block
create or replace function new_cnt_test_ho(in_table text, out out_table text, out cnt_rows int) returns setof record AS $$
DECLARE i text;
BEGIN
FOR i IN
select column_name
from information_schema."columns"
where table_schema = 'public'
and table_name = in_table
LOOP
execute '
select $1, count($1)
from '|| quote_ident(in_table) ||'
where $1 is not null '
INTO out_table, cnt_rows
using i, quote_literal(i), quote_ident(in_table), quote_literal(in_table) ;
return next;
END LOOP;
END;
$$LANGUAGE plpgsql
Result:
select * from new_cnt_test_ho('actor_new')
out_table |cnt_rows|
-----------+--------+
actor_id | 203|
first_name | 203|
last_name | 203|
last_update| 203|
There are 4 parameters specified in using, because I assumed that the error was in quotes, I took turns playing with arguments from 1 to 4
The correct result should be like this
out_table |cnt_rows|
-----------+--------+
actor_id | 203|
first_name | 203|
last_name | 200|
last_update| 200|

Answer 1

based on your title: input is a table name, output is a table one column is column name, another column is return of count(column)
first check the table exists or not.
then for loop get each column name, after that for each column name run a query.
a sample query is select 'cola',count(cola) from count_nulls. first occurrence is literal 'cola', so we need quote_literal(cols.column_name),
second is the column name, so we need use quote_ident(cols.column_name)
select 'cola',count(cola) from count_nulls will count column cola all not null value. if a column all value is null then return 0.
The following function will return the expected result. Can be simplified, since i use a lot of raise notice.
CREATE OR REPLACE FUNCTION get_all_nulls (_table text)
RETURNS TABLE (
column_name_ text,
numberofnull bigint
)
AS $body$
DECLARE
cols RECORD;
_sql text;
_table_exists boolean;
_table_reg regclass;
BEGIN
_table_reg := _table::regclass;
_table_exists := (
SELECT
EXISTS (
SELECT
FROM
pg_tables
WHERE
schemaname = 'public'
AND tablename = _table));
FOR cols IN
SELECT
column_name
FROM
information_schema.columns
WHERE
table_name = _table
AND table_schema = 'public' LOOP
_sql := 'select ' || quote_literal(cols.column_name) || ',count(' || quote_ident(cols.column_name) || ') from ' || quote_ident(_table::text);
RAISE NOTICE '_sql:%', _sql;
RETURN query EXECUTE _sql;
END LOOP;
END;
$body$ STRICT
LANGUAGE plpgsql;
setup.
begin;
create table count_nulls(cola int, colb int, colc int);
INSERT into count_nulls values(null,null,null);
INSERT into count_nulls values(1,null,null);
INSERT into count_nulls values(2,3,null);
commit;