内存优化表支持的collation

在SQL Server中，Collation 决定varchar 或 char字段的Byte representation和Code Page。在内存优化表中，字符类型（varchar，char，nvarchar，nchar）的column，必须使用Code Page=1252的Collation；如果 memory-optimized index 创建在字符类型的Column上，那么该column只能使用以 BIN2 结尾的collation。

限制1，在字符列(unicode和 non-nicode)上创建Memory-optimized index，那么该字符列必须使用BIN2 collation。

Collation ：Bosnian_Latin_100_BIN2 的Code Page 是1520，用于 LastName varchar(20) 时报错：The data types char(n) and varchar(n) using a collation that has a code page other than 1252 are not supported with memory optimized tables.

-- create a table with collation
CREATE TABLE dbo.Employees
(
  EmployeeID int NOT NULL ,
  LastName varchar(20) COLLATE Bosnian_Latin_100_BIN2 NOT NULL INDEX IX_LastName NONCLUSTERED,
  FirstName nvarchar(10) NOT NULL ,
  CONSTRAINT PK__Employees PRIMARY KEY NONCLUSTERED HASH(EmployeeID)  WITH (BUCKET_COUNT=1024)
)
WITH (MEMORY_OPTIMIZED=ON, DURABILITY=SCHEMA_AND_DATA)
GO

在内存优化表中，要在non-unicode字符列上创建index，必须满足两个条件：Collation Name 以 BIN2 结尾，Code Page是1252；要在unicode 字符列上创建Index，只需要满足一个条件：Collation Name 以BIN2 结尾。

Indexes on (n)(var)char columns can only be specified with BIN2 collations

-- all supported collations for indexes on memory-optimized tables and
-- comparison/sorting in natively compiled stored procedures
select *
from sys.fn_helpcollations()
where name like ‘%BIN2‘
    and collationproperty(name, ‘codepage‘) = 1252;

限制2 ，在内存优化表中，non-unicode 字符列的Code Page必须是1252。如果需要存储Code Page不是1252的字符，必须使用 unicode 数据类型。

(var)char columns in memory-optimized tables must use code page 1252 collation. This restriction does not apply to n(var)char columns. If you need to store non-Latin characters, use n(var)char columns.

-- all supported collations for (var)char columns in memory-optimized tables
select * from sys.fn_helpcollations()
where collationproperty(name, ‘codepage‘) = 1252;

引用《Collations and Code Pages》：

In-Memory OLTP has restrictions on supported code pages for (var)char columns in memory-optimized tables and supported collations used in indexes and natively compiled stored procedures.

The code page for a (var)char value determines the mapping between characters and the byte representation that is stored in the table. For example, with the Windows Latin 1 code page (1252; the SQL Server default), the character ‘a‘ corresponds to the byte 0x61.

The code page of a (var)char value is determined by the collation associated with the value. For example, the collation SQL_Latin1_General_CP1_CI_AS has the associated code page 1252.

The collation of a value is either inherited from the database collation, or can be specified explicitly using the COLLATE keyword. Database collation cannot be changed if the database contains memory-optimized tables or natively compiled stored procedures. The following example sets the database collation and creates a table, which has a column with a different collation. The database uses Latin case-insensitive collation.

Indexes can only be created on string columns if they use a BIN2 collation. The LastName variable uses BIN2 collation. FirstName uses the database default, which is CI_AS (case-insensitive, accent-sensitive).

示例：创建一个内存优化表，使用collate 子句显式指定字符列的Collation，然后在字符列上创建memory-optimized index。

use master
go 

--create database
create database TestMemoryDB;

--add filegroup
alter database TestMemoryDB
add FileGroup FG_TestMemoryDB
contains MEMORY_OPTIMIZED_DATA;

--add file
alter database TestMemoryDB
add file
(
    name=‘TestMemoryDBDirectory‘,
    filename=‘D:\MSSQLServerData\MSSQL12.MSSQLSERVER\MSSQL\DATA\TestMemoryDBDirectory‘
)
to FileGroup FG_TestMemoryDB;

--  set the database collations
ALTER DATABASE TestMemoryDB COLLATE Latin1_General_100_CI_AS
GO

USE TestMemoryDB
GO

-- create a table with collation
CREATE TABLE dbo.Employees
(
  EmployeeID int NOT NULL ,
  LastName varchar(20) COLLATE Latin1_General_100_BIN2 NOT NULL INDEX IX_LastName NONCLUSTERED,
  FirstName nvarchar(10) NOT NULL ,
  CONSTRAINT PK__Employees PRIMARY KEY NONCLUSTERED HASH(EmployeeID)  WITH (BUCKET_COUNT=1024)
)
WITH (MEMORY_OPTIMIZED=ON, DURABILITY=SCHEMA_AND_DATA)
GO

参考doc：

Collations and Code Pages