How to check all columns existing in a table?

Question

Hello.
I'm writing a function that returns average value of every numeric column existing in a database.
I have a general idea how to do it, but I need just one more thing, look at the expamle:
select table_name from user_tables where rownum=1
this allows me to select names of all tables, and then I can access them 1 by 1...
But now i have a little problem - how to access all the atributes in selected table in this way?
Oh, and I have a problem with this rownum... For example it works for 1 (shows 1st row - name of first table) but does not for 2, or greater number :(.
And expresions like rownum < 5 work, but rownum > 3 not :/. What may be the reason?
Thank you for help!
Regards.

Answer 1

user13483761 wrote:
Thanks a lot! This 3 atributes is all I need, its a way lot easier than I thought before. I simply use cursor loop and your advices.
Almost got working code - but there is 1 error telling that select is incorrect :/. Why is that?
create or replace
FUNCTION SHOW_ALL
RETURN VARCHAR2 IS
v_ret VARCHAR(100):='Null';
BEGIN
DECLARE
CURSOR cur_stats IS SELECT table_name, column_name, data_type
FROM user_tab_columns;
v_zdanie VARCHAR(100);
BEGIN
FOR v_cur IN cur_stats LOOP
IF v_cur.data_type = 'NUMBER'
THEN
strike
--> select 'In table ' || v_cur.table_name || ' average value of ' ||--
--> v_cur.column_name || ' is:' || avg(v_cur.column_name)--
--> into v_zdanie--
--> from v_cur.table_name;--
strike
>
dbms_output.put_line(v_zdanie);
END IF;
END LOOP;
RETURN v_ret;
END;
END SHOW_ALL;
select 'In table ' || v_cur.table_name || ' average value of ' ||
v_cur.column_name || ' is:' || avg(v_cur.column_name)
into v_zdanie
from v_cur.table_name;
sql_developer tells that this 'table or perspective does not exist' or sth like that, I translated from my native language.You are missing lot of things in the function, you are hard coding the return value to null?
What you should do is as below:
remove the part what you have written, i have strike that above. declare a variable your_select_statement VARCHAR2(1000);
your_select_statement := 'select nvl(avg('||v_cur.column_name||'),0) from '||v_cur.table_name;
execute immediate your_select_statement into v_zdanie;
dbms_output.put_line('In table ' || v_cur.table_name || ' average value of ' ||v_cur.column_name || ' is:' ||v_zdanie);