ALTER statement allows me to change a computed by field with a new formula referencing a field that is positioned higher than the computed by field, but when you extract the table metadata and try to run it, it crashes with "Column unknown." error.
create table a
( field2 numeric (9,2),
field1 computed by (field2 * 0.5));
alter table a add field3 numeric (9,2);
alter table a alter field1 computed by (field3 * 0.5); -- This works fine!!!
Step 3 works fine, but when you extract the DDL of the table and try to run it, it will
crash, since it will be extracted like:
CREATE TABLE A (
FIELD1 COMPUTED BY (field3 * 0.5),
This means that you may have a "good" database, but when you extract its metadata into a script to create another empty database, it will crash :-(
IMHO, the behavior should be consistent in the two scenarios so, or the table creation should succeed, or the ALTER should had failed.