Lookup Transformation Overview
The Lookup transformation is a passive or active transformation that looks up data in a flat file, logical data object, reference table, or relational table. The Lookup transformation can return one row or multiple rows from a lookup.
Before you create a Lookup transformation, create the lookup source. Import a flat file or relational database table as a physical data object. Or, create a logical data object or reference table to use as a lookup source. When you create a Lookup transformation, the Developer tool adds the columns from the data object or reference table as lookup ports in the transformation. After you create the transformation, configure one or more output ports to return the lookup results. Configure the lookup conditions and configure other lookup properties.
When you run a mapping or preview data, the Integration Service queries the lookup source. The Integration Service queries the lookup source based on the lookup ports in the transformation, the lookup properties, and the lookup condition. The Lookup transformation returns the result of the lookup to the target or another transformation.
You can configure a connected or unconnected Lookup transformation. A connected transformation connects to another transformation in the mapping. An unconnected transformation receives input from a :LKP expression in another transformation. If the Lookup transformation performs a lookup on a logical data object, you must configure a connected Lookup transformation. Connect the Lookup transformation input ports to an upstream transformation or to an upstream source. Connect the output ports to a downstream transformation or to a downstream target.
You can use multiple Lookup transformations in a mapping.
You can perform the following tasks with a Lookup transformation:
- •Get a related value. Retrieve a value from the lookup source based on a value in the input data. For example, the input data contains an employee ID. Retrieve the employee name from the lookup source by employee ID.
- •Retrieve multiple rows from a lookup source.
- •Perform a calculation. Retrieve a value from a lookup table and use the value in a calculation. For example, retrieve a sales tax percentage, calculate a tax, and return the tax to a target.
- •Perform an unconnected lookup with a :LKP expression in a transformation that accepts expressions. Filter the results with another expression in the transformation.
- •Parameterize the lookup source and the lookup condition to use a Lookup transformation in a dynamic mapping.