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Some of the history tables are implemented as normal SQL Server tables, and the information contained in them is stored in the Runtime database file (Run110Dat.mdf). Others are implemented as a special type of table called a remote table, or extension table. Extension tables do not actually exist in the database, but rather expose data that is stored in special history files (history blocks) on disk using OLE DB technology. For more information, refer to the Data Retrieval Subsystem section in the Wonderware Historian Concepts Guide.
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[Live], [History] and [AnalogSummaryHistory] tables are extension tables, while Tag is a SQL Server table.
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Querying the extension tables do not always behave as you would expect a SQL Server table to behave. In SQL Server Management Studio, the extension tables are listed under the INSQL or INSQLD linked servers under the Server objects tree item.
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To allow joins between the analog, string, and discrete tables, the analog and string views reference the OLE DB linked server "INSQL," while the discrete views reference the OLE DB linked server "INSQLD".