Data entering the data warehouse can be manipulated if required. This manipulation can occur at any stage but is supported via a number of methods during the Load stage. Load tables provide options to transform data. If multiple pass transformations are required, then a Load table can be created from another Load table, e.g. multiple Load tables can be supported in the data flow path.
The options available differ depending on the type of load but in most cases the after transformation and post load procedure can be utilized. Specifically:
Database Link Load |
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ODBC Based Load |
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File Based Load |
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Integration Services Load |
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Script Based Load |
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Externally Loaded |
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The Transformation tab of a column's properties is used to define during and after load transformations. It can only be one or the other for a specific column. One column can be used to build another, so an after can be based on the results of a during, if different columns are used.
The During transformations use Source Table columns. The After transformations use the Load Table columns.
All After transformations take place in the native SQL language of the data warehouse database. The During transformations differ in terms of which language is used. This is particularly true for file based loads. Normally the 'During' transformation will occur in the native SQL language of the source database.