在UPDATE期间触发列的默认值 [英] Trigger default value of a column during UPDATE

问题描述

我想知道Oracle 12c的这种情况；

I am wondering about this case with Oracle 12c;

1. 表X的A列为默认值'default'和NOT NULL修饰符
2. 我在表X中插入了新行，并且列A的值为'not-default'
3. 我希望将上一行的A列更新为给定列的默认值，即'default'

1. Table X has column A, with default value 'default' and NOT NULL modifier
2. I insert a new row into Table X, and column A has value 'not-default'
3. I wish to update column A of the above row to the default value of the given column, namely 'default'

有不知道默认值的简短方法吗?我可以做类似的事情吗?

Is there a short way of doing this without knowing the default value? Can I do something like;

UPDATE X SET A = DEFAULT_VAL(A) WHERE ...

尝试更新为null显然会触发ORA-01407: cannot update ("schema"."X"."A") to NULL，我想知道Oracle上是否有这样的功能.

Trying to update to null obviously triggers a ORA-01407: cannot update ("schema"."X"."A") to NULL, I'd like to know if there is such a feature on Oracle.

推荐答案

我们可以在update和insert语句中使用默认关键字. 例如

We can you default keyword in update and insert statement. eg

 update x set A = default where ...

这将对您的情况有帮助，在其他情况下，例如我不想在插入语句中添加列子句

This will be helpful for your case and also in another case like i don't want add column clause in insert statement like

insert into table values (val1, val2, default);

如果我们不能使用默认值，那么我们必须添加列子句，相同的查询将如下所示

If we couldn't use default then we have to add column clause, same query will be like below

insert into table (col1, col2, col3) values (val1, val2, default);

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