未强制执行唯一约束检查
create table A (id, field1, field2, field3, field4)
我对 field1、field2、field3 有一个唯一约束，并且以下记录存储在表中，
例如
insert into A (1, "f1", null, "f3", "f4");
insert into A (2, "f1", null, "f3", "f4");
insert into A (3, "f1", null, "f3", "f4");
我希望这会引发唯一的约束违规，因为所有记录都违反了，但事实并非如此。我在这里缺少什么，检查了数据库并且已经创建了唯一约束索引。
create table A (id, field1, field2, field3, field4)
I have a unique constraint on field1, field2, field3 and the following records are stored in the table
e.g.
insert into A (1, "f1", null, "f3", "f4");
insert into A (2, "f1", null, "f3", "f4");
insert into A (3, "f1", null, "f3", "f4");
I would expect this to throw an unique constraint violation since all records are in violation, but it doesn't. What am I missing here, did check the database and the unique constraint index has been created.
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Null值永远不会等于任何其他值，甚至null也是如此。null != null这就是为什么记录
a + null + b永远不会重复记录a + null + bNullvalue is never equal to any other value, evennulltoo.null != nullThat is why record
a + null + bwill be never duplicate recorda + null + b