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Sams Microsoft SQL Server 2008- P5

Tham khảo tài liệu 'sams microsoft sql server 2008- p5', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Types of Data Sources 181 Report-Specific Data Sources The report-specific data source should be used only when the data needed to process a report should be restricted to that report. If multiple reports need to access the same data source with the same credentials you should use a shared data source. This is because maintaining lots of embedded data sources can be cumbersome. After the report has been published to the Report Server the embedded data source has to be maintained as part of that report. You can use the Report Manager web interface to change the reference from an embedded to a shared data source. Shared Data Sources A shared data source exists on the Report Server as a separate entity. Report developers can define a shared data source in Visual Studio but it does not overwrite an existing data source by default in the same manner that it overwrites reports. To override a shared data source you have to set OverwriteDataSources project property to True see Figure 11.1 . 11 FIGURE 11.1 OverwriteDataSources project property. A shared data source is useful when Many reports use data from the same location with the same credentials. An administrator needs to have an easy way to change the location of a data source for several reports. This is the case for example when moving reports from development to production. Data Source Expressions An expression can be used to define the connection at runtime. A classic case is the difference between an active online transaction processing OLTP database and historical data or a data warehouse. Many companies store historical data that is more than six months lease purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 182 CHAPTER 11 Accessing Data old in a data warehouse. You would have to determine an appropriate connection from some report-level parameter. Like all expressions a data source expression would have to be written in Visual Basic.NET and preceded by an equals sign. To define data source .