How can i get a count(*) of all the columns in a table? Using PostgreSql

Question

I have bunch of tables where several of them have hundreds of columns. I need to get a count of non-null values for each column and I've been doing it manually. I would like to figure out a way to get all the counts for all the columns in a table. I looked up stackoverflow and google, but unable to find the answer.

I tried this but it's just returning a value of 1 for each column. I know it's just counting the number of column and not the values in each column. Any suggestions?

select count(COLUMN_NAME)
from information_schema.columns
where table_schema = 'schema_name'
and table_name = 'table_name'
group by COLUMN_NAME

Answer 1

COUNT(column_name) always gives you the count of NON NULL values.

Create a generic function like this which can take schema name and table name as arguments.

Here I am constructing select statements joined together by UNION ALLs each returning the value of the column_name and it's count for all columns when executed dynamically.

CREATE OR REPLACE FUNCTION public.get_count( TEXT, TEXT )
RETURNS  TABLE(t_column_name  TEXT, t_count BIGINT )
LANGUAGE plpgsql
AS $BODY$
DECLARE
p_schema        TEXT := $1;
p_tabname       TEXT := $2;
v_sql_statement TEXT;

BEGIN

SELECT STRING_AGG( 'SELECT ''' 
       || column_name 
       || ''',' 
       || ' count(' 
       || column_name 
       || ')  FROM ' 
       || table_schema 
       || '.' 
       || table_name 
         ,' UNION ALL ' ) INTO v_sql_statement
FROM   information_schema.columns 
WHERE  table_schema   = p_schema 
       AND table_name = p_tabname; 

    IF v_sql_statement IS NOT NULL THEN
     RETURN QUERY EXECUTE   v_sql_statement;
    END IF;
END
$BODY$;

Execution

knayak=# select c.col, c.count from 
 public.get_count( 'public', 'employees' ) as c(col,count);
      col       | count
----------------+-------
 employee_id    |   107
 first_name     |   107
 last_name      |   107
 email          |   107
 phone_number   |   107
 hire_date      |   107
 job_id         |   107
 salary         |   107
 commission_pct |    35
 manager_id     |   106
 department_id  |   106
(11 rows)