sql 数据处理时join字段慎重选择--避免出现double数据！

前几天做BI Tabular表格模型的时候，数据中心核对数据发现模型展现数据比实际数据要多，经过核查之后，发现原来我是一个不经意，在做数据选取的时候，inner join的字段CITY_NAME_CN选取错误。

首先对比事实表和我数据源选取的数据量差异：正常（8080945条记录）

SELECT  [GUID]
,[YYYYMMDD]
,[BRAND]
,[BRAND_GROUP]
,[MODEL]
,[CHANNEL]
,CASE [CHANNEL]WHEN 'NON-ITS'THEN'3C'WHEN 'INTERNET B2C'THEN'NC'WHEN 'ASSB'THEN'TC'WHEN 'CS'THEN'TC'ELSE'TC' END AS CHANNEL_TYPE_CODE
,[SALES_UNIT]
,[SALES_VALUE]
,[PC_TYPE]
,[DESIGN]
,[PROCESSOR_BRAND]
,[PROCESSOR]
,[PROCESSOR_NUMBE]
,[STORAGE_CAPAC]
,[RAM_MB]
,[DVD_WRITER]
,[SIZE_INCH]
,[GPU_BRAND]
,[GPU_MODEL]
,[ONBOARD_GRAPHIC]
,[V_RAM]
,[OS_PLANTFORM]
,[MICROSOFT_OS]
,[CATEGORIES]
,[PPC_PRICE_BRAND]
,[DPC_PRICE_BRAND]
,a.[CITY_NAME_CN]
,a.[CITY_NAME_EN]
,ISNULL(b.CITY_CODE,0)AS CITY_CODE
,[BU_GROUP_CODE]
,A.[CITY_FULL_NAME_CN]
,Form_Factor
,isnull(CITY_GROUP,'')as CITY_GROUP
FROM [DM_ACCN_T1].[dbo].[FS_MS_GFK] A
LEFT JOIN  [DM_ACCN_T1].[dbo].[CB_GEOGRAPHY] B ON A.CITY_FULL_NAME_CN=B.CITY_FULL_NAME

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