例子:l_amount_temp是临时字段, L_AMOUNT是要修改的字段.
alter table LAW_LITIGATION_CASE add l_amount_temp int;
alter table LAW_LITIGATION_CASE modify L_AMOUNT NULL;
update LAW_LITIGATION_CASE set l_amount_temp=L_AMOUNT,L_AMOUNT=NULL;
commit;
alter table LAW_LITIGATION_CASE modify L_AMOUNT float(24);
update LAW_LITIGATION_CASE set L_AMOUNT= l_amount_temp, l_amount_temp=NULL;
commit;
alter table LAW_LITIGATION_CASE drop column l_amount_temp;
alter table LAW_LITIGATION_CASE modify L_AMOUNT NOT NULL;