Neo4j 唯一性约束与索引问题

我一定是做错了什么，或者对约束和索引有误解。我有以下资料：

CREATE CONSTRAINT ON (u:User) ASSERT u.user_id IS UNIQUE

及

我试过改变顺序，但不管怎样，我得到了：

Neo.ClientError.Schema.ConstraintAlreadyExists

或

视订购情况而定

我不明白为什么我不能这样做。我想快速查找

用户id

，这就是我编制索引的原因，我还想确保

用户id

是唯一的，这就是我有一个约束的原因

---

我误解了什么？我应该怎么做呢？

添加唯一约束也会在该属性上添加索引-因此唯一约束就足够了

看

“请注意，在属性上添加唯一性约束也会增加 该属性上的索引，因此不能单独添加此类索引。 Cypher将使用该索引进行查找，就像其他索引一样 如果删除一个约束，但仍然需要属性上的索引，则 必须创建索引。”

---

创建约束将自动在该属性上创建索引。如果仅创建索引，则必须手动创建索引

---

正如Luane所说，在属性上添加唯一性约束也会在属性上创建索引

要使

用户id

唯一并建立索引，应使用以下命令：

CREATE CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Added 1 constraint, returned 0 rows in 107 ms

:SCHEMA

>>> Indexes
>>>   ON :User(user_id)             ONLINE (for uniqueness constraint) 
>>> 
>>> Constraints
>>>   ON (user:User) ASSERT user.user_id IS UNIQUE

DROP INDEX ON :User(user_id)

>>> Unable to drop index on :User(user_id): Index belongs to constraint: :User(user_id)

DROP CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Removed 1 constraint, returned 0 rows in 108 ms

要验证索引是否已正确添加：

CREATE CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Added 1 constraint, returned 0 rows in 107 ms

:SCHEMA

>>> Indexes
>>>   ON :User(user_id)             ONLINE (for uniqueness constraint) 
>>> 
>>> Constraints
>>>   ON (user:User) ASSERT user.user_id IS UNIQUE

DROP INDEX ON :User(user_id)

>>> Unable to drop index on :User(user_id): Index belongs to constraint: :User(user_id)

DROP CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Removed 1 constraint, returned 0 rows in 108 ms

注意，如果您试图删除由唯一性约束自动创建的索引，它将失败：

CREATE CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Added 1 constraint, returned 0 rows in 107 ms

:SCHEMA

>>> Indexes
>>>   ON :User(user_id)             ONLINE (for uniqueness constraint) 
>>> 
>>> Constraints
>>>   ON (user:User) ASSERT user.user_id IS UNIQUE

DROP INDEX ON :User(user_id)

>>> Unable to drop index on :User(user_id): Index belongs to constraint: :User(user_id)

DROP CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Removed 1 constraint, returned 0 rows in 108 ms

删除它的正确方法是删除唯一性约束：

CREATE CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Added 1 constraint, returned 0 rows in 107 ms

:SCHEMA

>>> Indexes
>>>   ON :User(user_id)             ONLINE (for uniqueness constraint) 
>>> 
>>> Constraints
>>>   ON (user:User) ASSERT user.user_id IS UNIQUE

DROP INDEX ON :User(user_id)

>>> Unable to drop index on :User(user_id): Index belongs to constraint: :User(user_id)

DROP CONSTRAINT ON (user:User) ASSERT user.user_id IS UNIQUE

>>> Removed 1 constraint, returned 0 rows in 108 ms

---

完全没有注意到这一点。非常感谢你！