例子:l_amount_temp是临时字段, L_AMOUNT是要修改的字段.

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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;