比如：create table tb(t1 int,t2 int,t3 int , t4 int)
我想把t4改成计算列 t4=t1+t2+t3,怎么修改这列，修改语句怎么写
------解决方案--------------------
update tb set t4=t1+t2+t3
------解决方案--------------------
update tb set t4=nvl(t1,0)+nvl(t2,0)+nvl(t3,0);
------解决方案--------------------
如果你需要的是建立一个虚拟列,那么只能先将这一列删除,然后再创建一个新的虚拟列
- SQL code
SQL> create table tb(t1 int,t2 int,t3 int , t4 int) ;Table created.SQL> create table tb(t1 int,t2 int,t3 int , t4 int) ;Table created.SQL> commit ;Commit complete.SQL> alter table tb modify t4 as (t1+t2+t3) ;alter table tb modify t4 as (t1+t2+t3) *ERROR at line 1:ORA-54026: Real column cannot have an expressionSQL> alter table tb drop column t4 ;Table altered.[color=#FF0000]SQL> alter table tb add t4 as (t1+t2+t3) ;[/color]Table altered.SQL> select * from tb ; T1 T2 T3 T4---------- ---------- ---------- ---------- 1 1 1 3 2 2 2 6 3 3 3 9 4 4 4 12 5 5 5 15 6 6 6 18 7 7 7 21 8 8 8 24 9 9 9 27 10 10 10 3010 rows selected.