Question

I have two tables  
1.
shiv_tab_col

TABLENAME     | COLUMNNAME
--------------------------  
 SER_SHIV_SYN | TABLENAME    
 SER_SHIV_SYN | COLUMNNAME


AND SER_SHIV_SYN

TABLENAME   | COLUMNNAME
--------------------------  
 A          |  B  
 E          | NULL  
NULL        | NULL  
NULL        | NULL  
NULL        | NULL  
NULL        | NULL  

BUT WHEN I M TRYING TO RUN THE BELOW CODE IT IS GIVING ME '0' AS VALUE OF TNAME

DECLARE
tname varchar(20):=null;

 CURSOR C1 IS
    SELECT  *
    FROM SHIV_TAB_COL;


BEGIN
    for rec in C1

loop
    select count(*) into tname from (select nvl(rec.columnname,1)b from ser_shiv_syn) where b ='1';
    dbms_output.put_line(tname);
    dbms_output.put_line(rec.columnname);
END LOOP;
END;

Actually i m looking to count the no. of null values in each column which will be stored in variable TNAME
for first column it should give 4
for 2 column it should give 5

Answer 1

What you are doing now is counting all empty occurrences of the column COLUMNNAME in the table shiv_tab_col. Which is 0 (you already found that out).

The solution is a bit more complicated, you need dynamic SQL to accomplish what you want to do:

declare
  l_count pls_integer;
begin
  for r_cur in (
    select columnname
    from shiv_tab_col
  )
  loop
    execute immediate 
      'select count(1) from ser_shiv_syn where '||r_cur.columnname||' is null' 
    into l_count;
    dbms_output.put_line(l_count);
    dbms_output.put_line(r_cur.columnname);
  end loop;
end;
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