统计--VARCHAR与NVARCHAR在统计预估上的区别

DROP TABLE TB101
GO
DROP TABLE TB102
GO
SELECT 
CAST(NCHAR(19968+20902*RAND(RID))+NCHAR(19968+20902/2*RAND(RID))+NCHAR(19968+20902/3*RAND(RID)) AS varchar(40)) AS RName
,*
INTO TB101
FROM(
SELECT ROW_NUMBER()OVER(ORDER BY T1.OBJECT_ID DESC) AS RID,T1.* FROM sys.all_objects T2
CROSS JOIN sys.all_columns T1
) AS T
WHERE T.RID<1000000
GO
SELECT * INTO TB102 FROM TB101
GO
ALTER TABLE TB102
ALTER COLUMN RName NVARCHAR(40)
GO
CREATE UNIQUE CLUSTERED INDEX IDX_RID ON TB101(RID)
GO
CREATE UNIQUE CLUSTERED INDEX IDX_RID ON TB102(RID)
GO
CREATE INDEX IDX_Name ON TB101(RName)
GO
CREATE INDEX IDX_Name ON TB102(RName)
GO

EXEC sp_spaceused ‘TB101‘
EXEC sp_spaceused ‘TB102‘
GO

SELECT * FROM TB101
WHERE RName LIKE ‘你好%‘

SELECT * FROM TB102
WHERE RName LIKE N‘你好%‘