External tables

An external table is a data file that is not managed by the HCL Informix® database server. The definition of the external table includes data-formatting type, external data description fields, and global parameters.

To map external data to internal data, the database server views the external data as an external table. Treating the external data as a table provides a powerful method for moving data into or out of the database and for specifying transformations of the data.

When the database server runs a load task, it reads data from the external source and performs the conversion required to create the row and then inserts the row into the table. The database server writes errors to a reject file.

If the data in the external table cannot be converted, you can specify that the database server write the record to a reject file, along with the reason for the failure. To do this, you specify the REJECTFILE keyword in the CREATE EXTERNAL TABLE statement.

The database server provides a number of different conversion mechanisms, which are performed within the database server and therefore provide maximum performance during the conversion task. The database server optimizes data conversion between ASCII and HCL Informix data representations, in both fixed and delimited formats.

To perform customized conversions, you can create a filter program that writes converted data to a named pipe. The database server then reads its input from the named pipe in one of the common formats.

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