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;
sys.index_columns中的key_ordinal列以与复合主键中声明的顺序相同的顺序显示索引列:
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';
DBCC SHOW_STATISTICS ('Foo',PK_Foo);
但是,sys.stats_columns显示以反向顺序列出的列(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表示stats_column_id是“stats列集中的基于1的序数”,因此我期望值1指向统计对象中的第一列.
这是sys.stats_columns中的错误还是我的误解?
我已经验证了此行为发生在sql Server 2005,2008,2008 R2,2012和2014的当前版本上.
sys.stats_columns似乎反映了统计对象在其他情况下的顺序,例如:
CREATE TABLE dbo.Foo2( ID1 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,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%';
这是另一个示例,其中sys.stats_columns似乎返回正确的数据,这次是对索引的统计信息:
--drop table dbo.Foo3 CREATE TABLE dbo.Foo3( ID1 int NOT NULL,CONSTRAINT [PK_Foo3] PRIMARY KEY CLUSTERED (ID2,ID1) ); GO INSERT INTO Foo3 (ID1,'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,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%';
解决方法
swasheck – 2015年3月5日发布:
https://connect.microsoft.com/SQLServer/feedback/details/1163126
MSDN notes that sys.stats_columns.stats_column_id is “1-based ordinal
within set of stats columns.” However,it seems to actually reflect
table deFinition order. Altering index order is not reflected in
sys.stats_columns.
Max Vernon和James Lupolt似乎同意他们的评论/鼓励.
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