How to truncate all user tables?

declarebeginfor c1 in (select table_name, constraint_name from user_constraints) loop    begin        execute immediate ('alter table '||c1.table_name||' disable constraint '||c1.constraint_name);    end;end loop;for t1 in (select table_name from user_tables) loop    begin        execute immediate ('truncate table '||t1.table_name);    end;end loop;for c2 in (select table_name, constraint_name from user_constraints) loop    begin        execute immediate ('alter table '||c2.table_name||' enable constraint '||c2.constraint_name);    end;end loop;end;/

Improved the above script in case you can't remove the constraint because dependencies exist (in the form of foreign keys that are dependent on this constraint - ORA-02297.) and by printing all (disable, truncate and enable) statements.

set serveroutput on;declarebeginfor c1 in (select y1.table_name, y1.constraint_name from user_constraints y1, user_tables x1 where x1.table_name = y1.table_name order by y1.r_constraint_name nulls last) loop    begin        dbms_output.put_line('alter table '||c1.table_name||' disable constraint '||c1.constraint_name || ';');        execute immediate  ('alter table '||c1.table_name||' disable constraint '||c1.constraint_name);    end;end loop;for t1 in (select table_name from user_tables) loop    begin        dbms_output.put_line('truncate table '||t1.table_name || ';');            execute immediate ('truncate table '||t1.table_name);    end;end loop;for c2 in (select y2.table_name, y2.constraint_name from user_constraints y2, user_tables x2 where x2.table_name = y2.table_name order by y2.r_constraint_name nulls first) loop    begin        dbms_output.put_line('alter table '||c2.table_name||' enable constraint '||c2.constraint_name || ';');                execute immediate ('alter table '||c2.table_name||' enable constraint '||c2.constraint_name);    end;end loop;end;

Improvement in case you have special constraints which make above script fail:

set serveroutput on;declarebeginfor c1 in (select y.table_name, y.constraint_name from user_constraints y, user_tables x where x.table_name = y.table_name) loop    begin        dbms_output.put_line('alter table '||c1.table_name||' disable constraint '||c1.constraint_name || ';');        execute immediate  ('alter table '||c1.table_name||' disable constraint '||c1.constraint_name);    end;end loop;for t1 in (select table_name from user_tables) loop    begin        execute immediate ('truncate table '||t1.table_name);    end;end loop;for c2 in (select table_name, constraint_name from user_constraints) loop    begin        execute immediate ('alter table '||c2.table_name||' enable constraint '||c2.constraint_name);    end;end loop;end;/