sql - 数据压缩 SQL Server 2008 R2

Question

我有PAGE压缩类型的表，它的大小是 7 GB。但是当我使用

sp_estimate_data_compression_savings 'dbo', 'tableName', null, null, 'PAGE'

它返回size_with_requested_compression_setting - 3GB，降低当前表的大小。

我不明白为什么压缩表中的空间节省估计。

建表脚本：

    CREATE TABLE [dbo].[_AccumRgT2225](
    [_Period] [datetime] NOT NULL,
    [_Fld2217RRef] [binary](16) NOT NULL,
    [_Fld5936RRef] [binary](16) NOT NULL,
    [_Fld2218RRef] [binary](16) NOT NULL,
    [_Fld5937RRef] [binary](16) NOT NULL,
    [_Fld2219] [datetime] NOT NULL,
    [_Fld2220] [numeric](21, 2) NOT NULL
) ON [PRIMARY]

GO
CREATE UNIQUE CLUSTERED INDEX [_AccumR2225_ByDims_TRRRRT] ON [dbo].[_AccumRgT2225]
(
    [_Period] ASC,
    [_Fld2217RRef] ASC,
    [_Fld5936RRef] ASC,
    [_Fld2218RRef] ASC,
    [_Fld5937RRef] ASC,
    [_Fld2219] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO