Change the datatype of all the columns

Question

Oracle version 10g.
I have a table with 150 columns.
I'd like to change the datatype of all the columns in my table to varchar.
Do we have a query for this task?
Thanks.

Answer 1

Not knowing yet what you'll answer to John:
If your table is empty, you can use the datadictionary to generate a statement and execute it using dynamic SQL or spool the query to a file that does the DDL and run that...
Example:
MHO%xe> create table bla (col1 number, col2 number);
Tabel is aangemaakt.
MHO%xe> select column_name, data_type from user_tab_columns where table_name = 'BLA';
COLUMN_NAME                    DATA_TYPE
COL1                           NUMBER
COL2                           NUMBER
MHO%xe> declare
  2    l_sql varchar2(4000);
  3    l_sep varchar2(1);
  4  begin
  5    l_sql := 'alter table BLA modify ('||chr(10);
  6    for rec in ( select column_name from user_tab_columns where table_name = 'BLA')
  7    loop
  8      l_sql := l_sql||l_sep||' '||rec.column_name||' varchar2(50)'||chr(10);
  9      l_sep := ',';
10    end loop;
11    --
12    dbms_output.put_line(l_sql||' )');
13    --
14    execute immediate l_sql||' )';
15    --
16  end;
17  /
alter table BLA modify (
COL1 varchar2(50)
, COL2 varchar2(50)
PL/SQL-procedure is geslaagd.
MHO%xe> select column_name, data_type from user_tab_columns where table_name = 'BLA';
COLUMN_NAME                    DATA_TYPE
COL1                           VARCHAR2
COL2                           VARCHAR2