Sql Server Unique Key也是索引吗？ [英] Is the Sql Server Unique Key also an Index?
问题描述
我在表中有一个列（例如UserName），我想确保它是唯一的。所以我为该列创建了一个唯一的密钥，并将其命名为IX_Users_UserName。
I've got a column in a table (eg. UserName) which I want to make sure is unique. So I create a unique key for that column and call it IX_Users_UserName.
现在，如果我根据用户名进行大量搜索，我想确保有用户该字段的索引。
Now, if I do lots of searching for users based on their username I want to make sure there is an index for that field.
我是否需要创建单独的索引，或者是唯一的密钥也被视为索引，就像主键是群集唯一键一样？
Do I need to create a separate index, or is the unique key also considered an index, just like the primary key is a clustered unique key?
推荐答案
唯一键：唯一键强制执行
列的唯一性
已定义。 Unique Key在列上创建
非聚集索引。
唯一键只允许一个NULL值。
Unique Key: Unique Key enforces uniqueness of the column on which they are defined. Unique Key creates a non-clustered index on the column. Unique Key allows only one NULL Value.
更改表以向列添加唯一约束
：
Alter table to add unique constraint to column:
ALTER TABLE作者ADD CONSTRAINT
IX_Authors_Name UNIQUE（名称）GO
ALTER TABLE Authors ADD CONSTRAINT IX_Authors_Name UNIQUE(Name) GO
More information from MSDN.
FWIW - 如果您的约束没有创建索引，我会避免命名它 IX _ 因为通常会假设它与一个相关联（IX =指数）。
FWIW -- if your constraint doesn't create an index, I would avoid naming it IX_ as that would typically be assumed to be associated with one (IX = Index).
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