sql-server - AspNetUserLogins 表和 SQL Server 中索引键的最大大小

Question

VS2017/aspnetcore中身份模型的schema定义了一个叫做AspNetUserLogins的表来存储外部登录信息(下面的CREATE语句)。它将主键定义为 [LoginProvider] [nvarchar] (450) 和 [ProviderKey] [nvarchar] (450) 的组合。 SQL 服务器对索引键最大大小的限制指定为 900 字节 here .该页面上的注释特别说明

"If a table column is a Unicode data type such as nchar or nvarchar, the column length displayed is the storage length of the column. This is two times the number of characters specified in the CREATE TABLE statement. In the previous example, City is defined as an nvarchar(30) data type; therefore, the storage length of the column is 60."

那么这个 key 不是允许大小的两倍吗？

Sql Server Management Studio 好像也是这么认为的....

Warning! The maximum key length for a clustered index is 900 bytes. The index 'PK_AspNetUserLogins' has maximum length of 1800 bytes. For some combination of large values, the insert/update operation will fail.

CREATE TABLE [dbo].[AspNetUserLogins](
    [LoginProvider] [nvarchar](450) NOT NULL,
    [ProviderKey] [nvarchar](450) NOT NULL,
    [ProviderDisplayName] [nvarchar](max) NULL,
    [UserId] [nvarchar](450) NOT NULL,
 CONSTRAINT [PK_AspNetUserLogins] PRIMARY KEY CLUSTERED 
(
    [LoginProvider] ASC,
    [ProviderKey] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

Answer 1

看起来他们知道... issue1451