Informatica Lookup Transformation组件的Connect 与Unconnected类型用法及区别：下面是通一个Lookup在不同Mapping中的使用：
1. Connect lookup： 可以返回多个输出port的字段值，需要用连接线将输入、输出port连接到其他组件。
2. Unconnected lookup 只能返回一个port的字段值，无需连接线连接到其他组件，只需直接在Expression表达式中像调用函数函数那样调用它即可获得返回值。
Connected and Unconnected Lookups
You can configure a connected Lookup transformation or an unconnected Lookup transformation. A connected Lookup transformation is a transformation that has input and output ports that you connect to other transformations in a mapping. An unconnected Lookup transformation appears in the mapping, but is not connected to other transformations.
An unconnected Lookup transformation receives input from the result of a :LKP expression in a transformation such as an Expression transformation or Aggregator transformation. The :LKP expression passes parameters to the Lookup transformation and receives a result back from the lookup. The :LKP expression can pass lookup results to another expression in the transformation to filter results.
The following table lists the differences between connected and unconnected lookups:
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Connected Lookup
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Unconnected Lookup
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Receives input values directly from the pipeline.
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Receives input values from the result of a :LKP expression in another transformation.
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Use a dynamic or static cache.
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Use a static cache.
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Cache includes the lookup source columns in the lookup condition and the lookup source columns that are output ports.
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Cache includes all lookup and output ports in the lookup condition and the lookup/return port.
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Returns multiple columns from the same row or insert into the dynamic lookup cache.
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Returns one column from each row to a return port.
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If there is no match for the lookup condition, the Integration Service returns the default value for all output ports. If you configure dynamic caching, the Integration Service inserts rows into the cache or leaves it unchanged.
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If there is no match for the lookup condition, the Integration Service returns NULL.
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If there is a match for the lookup condition, the Integration Service returns the result of the lookup condition for all lookup/output ports. If you configure dynamic caching, the Integration Service either updates the row the in the cache or leaves the row unchanged.
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If a match occurs for the lookup condition, the Integration Service returns the result of the lookup condition to the return port.
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Passes multiple output values to another transformation. Link lookup/output ports to another transformation.
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Returns one output value to another transformation. The Lookup transformation return port passes the value to the port that contains the :LKP expression in the other transformation.
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Supports user-defined default values.
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Does not support user-defined default values.
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