updating values in a loop by column name

Question

I have a table with several columns, and I would like to eliminate spaces value (' ') from the values. The query is:

update table
set column_name = trim(both ' ' from column_name)
where column_name like '% '

and since the table contains around 55 columns so probably a loop would be a feasible idea instead of writing update statement for each and every column.

First I checked if looping is working:

declare
    column_name varchar2(2048);
    cursor pointer is
         select column_name into column_name from user_tab_cols where table_name = 'TABLE_NAME';

begin 
    for x in pointer
    loop
        dbms_output.put_line(x.column_name);
    end loop;
end;

yes, it is working. I get column names in dbms_output window.

Now, Here is what I am trying to do which doesn't seem to work:

declare
    column_var varchar2(2048);
    cursor pointer is
         select column_name into column_var from user_tab_cols where table_name = 'TABLE_NAME';

begin 
    for x in pointer
    loop
         update table_name
         set x.column_var = trim(both ' ' from x.column_var)
         where x.column_var like '% ';
         commit;
    end loop;
end;

This is, unfortunately not working. This is error I get:

ORA-06550: line 11, column 18:
PLS-00302: component 'COLUMN_VAR' must be declared.
ORA-06550: line 11, column 16:
PL/SQL: ORA-00904: "X"."COLUMN_VAR": invalid identifier
ORA-06550: line 9, column 10:
PL/SQL: SQL Statement ignored

Any idea where I am going off the track?

Thanks in advance :-)

Answer 1

You need to use dynamic sql for this

    BEGIN
      FOR t IN (select column_name from user_tab_cols where table_name = 'MyTable')
                   LOOP
     EXECUTE IMMEDIATE
         'update MyTable set '||t.column_name||' = trim(both '' '' from '||t.column_name||') where '||t.column_name||' like ''% ''';

      END LOOP;

    END;

/

Answer 2

I think you need to provide the actual column name, rather than the string representing the column name in the statement. Would an execute immediate work for you?

declare
    column_var varchar2(2048);
    cursor pointer is
         select column_name into column_var from user_tab_cols where table_name = 'TABLE_NAME';

begin 
   for x in pointer
   loop
         execute immediate 
             'update table_name ' ||
             'set '|| x.column_var ||' = trim(both '' '' from '|| x.column_var ||')'||
             'where '|| x.column_var ||' like ''% ''';
         commit;
    end loop;
end;