将NVARCHAR2类型改为clob字段类型

alter table DM_SELF_PROGRAM rename column document to my_document;
alter table DM_SELF_PROGRAM add document clob;
update DM_SELF_PROGRAM set document = my_document;
alter table DM_SELF_PROGRAM drop column my_document;
comment on column DM_SELF_PROGRAM.document is '文件';
alter table DM_SELF_PROGRAM rename column d