in teradata ,DDL alter table can not only add column but also can alter column length in specific case
eg.
DDL:
create table bbb
(col1 varchar(10),
col2 varchar(20)
)
DML:
alter table bbb ADD col2 varchar(100)
RESULT:
ALTER TABLE completed. Elapsed Time = 00:00:00
but, in the case , if the column is defined char but not varchar
DDL:
create table aaa
(col1 char(10),
col2 char(20)
)
DML:
ALTER table aaa ADD col2 VARCHAR(15)
RESULT:
ALTER TABLE Failed. [3558] Cannot alter the specified attribute(s) for COL2.
as we see, modify column length by "alter table ", the conditions are strictly limited.
so, usually, we create a new table with the new defined column length ,then do a ins-sel and finally rename the table.
