sys.stats_columns 不正确吗？

Question

假设我有一个Foo包含列ID1, ID2和一个复合主键的表ID2, ID1。（我目前正在使用 System Center 产品，该产品具有以这种方式定义的多个表，主键列以它们在表定义中出现的相反顺序列出。）

CREATE TABLE dbo.Foo(
  ID1 int NOT NULL,
  ID2 int NOT NULL,
CONSTRAINT [PK_Foo] PRIMARY KEY CLUSTERED (ID2, ID1)
);
GO

-- Add a row and update stats so that histogram isn't empty
INSERT INTO Foo (ID1, ID2) VALUES (1,2);
UPDATE STATISTICS dbo.Foo;

的key_ordinal列sys.index_columns示出了它们在复合材料中的主键被宣布相同顺序的索引列：

SELECT t.name, i.name, c.column_id, c.name, ic.index_column_id, ic.key_ordinal
FROM sys.tables AS t
JOIN sys.indexes AS i
ON t.[object_id] = i.[object_id]
JOIN sys.index_columns AS ic
ON ic.[object_id] = i.[object_id]
AND ic.index_id = i.index_id
JOIN sys.columns AS c
ON ic.column_id = c.column_id
AND ic.[object_id] = c.[object_id]
WHERE t.name = 'Foo';

直方图还以相同的顺序显示统计信息：

DBCC SHOW_STATISTICS ('Foo',PK_Foo);

但是，sys.stats_columns显示以相反顺序列出的列 ( ID1, ID2)。

SELECT s.name, sc.stats_column_id, c.name
FROM sys.stats AS s
JOIN sys.stats_columns AS sc 
ON s.stats_id = sc.stats_id 
AND s.[object_id] = sc.[object_id] 
JOIN sys.columns AS c 
ON c.[object_id] = s.[object_id]
AND c.column_id = sc.column_id
JOIN sys.objects AS o 
ON o.[object_id] = c.[object_id] 
WHERE o.name = 'Foo'
AND s.name = 'PK_Foo';

Books Online说stats_column_id是“一组 stats 列中的基于 1 的序数”，所以我期望值 1 指向统计对象中的第一列。

这是sys.stats_columns我的错误还是我的误解？

我已经验证了在当前版本的 SQL Server 2005、2008、2008 R2、2012 和 2014 上会发生这种行为。

sys.stats_columns 似乎反映了其他情况下统计对象内的顺序，例如：

CREATE TABLE dbo.Foo2(
  ID1 int NOT NULL,
  ID2 int NOT NULL,
  ID3 int NULL,
  String VARCHAR(10) NULL,
CONSTRAINT [PK_Foo2] PRIMARY KEY CLUSTERED (ID2, ID1)
);

GO

INSERT INTO Foo2 (ID1, ID2, ID3, String) VALUES (1,2,3,'String');

CREATE STATISTICS ST_Test ON Foo2 (ID3, String);
CREATE STATISTICS ST_Test2 ON Foo2 (String, ID3);

DBCC SHOW_STATISTICS ('Foo2',ST_Test);
DBCC SHOW_STATISTICS ('Foo2',ST_Test2);


SELECT s.name, sc.stats_column_id, c.name
FROM sys.stats AS s
JOIN sys.stats_columns AS sc 
ON s.stats_id = sc.stats_id 
AND s.[object_id] = sc.[object_id] 
JOIN sys.columns AS c 
ON c.[object_id] = s.[object_id]
AND c.column_id = sc.column_id
JOIN sys.objects AS o 
ON o.[object_id] = c.[object_id] 
WHERE o.name = 'Foo2'
AND s.name LIKE 'ST_Test%';

这是另一个sys.stats_columns似乎返回正确数据的示例，这次是针对索引的统计信息：

--drop table dbo.Foo3
CREATE TABLE dbo.Foo3(
  ID1 int NOT NULL,
  ID2 int NOT NULL,
  ID3 int NULL,
  String VARCHAR(10) NULL,
CONSTRAINT [PK_Foo3] PRIMARY KEY CLUSTERED (ID2, ID1)
);

GO

INSERT INTO Foo3 (ID1, ID2, ID3, String) VALUES (1,2,3,'String');
UPDATE STATISTICS Foo3;

CREATE INDEX IX_Test ON Foo3 (ID3, String);
CREATE INDEX IX_Test2 ON Foo3 (String, ID3);

DBCC SHOW_STATISTICS ('Foo3',IX_Test);
DBCC SHOW_STATISTICS ('Foo3',IX_Test2);

SELECT s.name, sc.stats_column_id, c.name
FROM sys.stats AS s
JOIN sys.stats_columns AS sc 
ON s.stats_id = sc.stats_id 
AND s.[object_id] = sc.[object_id] 
JOIN sys.columns AS c 
ON c.[object_id] = s.[object_id]
AND c.column_id = sc.column_id
JOIN sys.objects AS o 
ON o.[object_id] = c.[object_id] 
WHERE o.name = 'Foo3'
AND s.name LIKE 'IX_Test%';

Answer 1

这似乎是一个长期存在的错误：

swasheck - 2015 年 3 月 5 日发布：

https://connect.microsoft.com/SQLServer/feedback/details/1163126

MSDN 指出 sys.stats_columns.stats_column_id 是“统计列集中的基于 1 的序数”。但是，它似乎实际上反映了表定义顺序。更改索引顺序未反映在 sys.stats_columns 中。

Max Vernon 和 James Lupolt 基于他们的评论/鼓励似乎同意。