Source Qualifier transformation act as virtual sources in Informatica. When you drag a relational table or flat file in Mapping Designer, the Source Qualifier transformation comes along with it. A source qualifier is the point where the Informatica processing actually starts. The extraction process starts from the source qualifier.

Note that it is always recommended that the columns of source and source qualifier match. Do not change the columns or their data type in the source qualifier. You can note the data type difference in the source definition and source qualifier, which is because Informatica interprets the data in that way itself.

To discuss the source qualifier, let's take an example of the Joiner transformation mapping we created earlier.

As you can see, there are two Source Qualifier transformations present in the mapping: one for flat file and the other for a relational database. You can see that we have connected only three columns from the Source...