列不为空可延迟
在 Oracle 中，延迟约束仅在提交时检查。
在 NOT NULL 约束的情况下 DEFERRABLE 子句的含义是什么？ 例如，
create table test(a number not null deferrable, b number);
insert into test(a,b) values (222, 111);
commit;
在这些语句之后，我认为以下代码可以工作
update test set a = null where b = 111;
delete test where b = 111;
commit;
，但事实并非如此。
两个定义有什么区别？
create table test1(a number not null deferrable, b number);
create table test2(a number not null, b number);
In Oracle deferred constraints are checked only at the point of commit.
What is the meaning of DEFERRABLE clause in a case of NOT NULL constraint?
For example
create table test(a number not null deferrable, b number);
insert into test(a,b) values (222, 111);
commit;
After these statements I thought the following code would work
update test set a = null where b = 111;
delete test where b = 111;
commit;
But it doesn't.
What is the difference between two definitions?
create table test1(a number not null deferrable, b number);
create table test2(a number not null, b number);
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这里有两个选择。您需要使用下面所示的命令在事务中设置要延迟的约束。
这应该在执行您定义的
UPDATE语句之前运行。或者，您可以在表定义中将约束设置为 INITIALLY DEFERRED
完成上述任一操作后，您应该能够运行问题中的 DML。
There are two options here. Either you need to set the constraint to be deferred within the transaction by using the command shown below
This should be run before doing the
UPDATEstatement that you have defined.Alternatively you can set the constraint to be
INITIALLY DEFERREDin the table definitionAfter doing either of these things, you should then be able to run the DML that you have in the question.