请问constraint中：not deferrable与 deferrable initially immediate 有何区别？谢谢

33281

创建constraint时有这样一个选项：

not deferrable | deferrable [ initially { immediate | deferred } ]

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not deferrable与 deferrable initially immediate

岂不都是check at the end of every DML statement，

请问两种状态有何区别？谢谢各位前辈。

csdn1234

not deferrable 与initially immediate是一样的,与deferrable initially immediate则不同。后者允许将constraint再改为initially deferred, 前者不允许更改:
>create table test2 (f1 number(3) constraint fk references test(f1) initially immediate);
>alter table test2 modify constraint fk initially deferred;
alter table test2 modify constraint fk initially deferred
*
ERROR 位于第 1 行:
ORA-02447: 无法延迟不可延迟的约束条件

> create table test2 (f1 number(3) constraint fk references test(f1) deferrable initially immediate);
> alter table test2 modify constraint fk initially deferred;
表已更改。

wysfenghuo007

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