create table liu(a varchar2(20),b number(2))

alter table liu rename to jin

rename jin to cai

alter table cai add  c varchar2(30)

alter table cai add  (d varchar2(30),e number(4))

alter table cai rename column e  to f

alter table cai modify d varchar(40)

alter table cai modify f varchar(40)

alter table cai drop column  f

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