When you specify a relational source table in the dataflow, Data Services executes simple SQL
SELECT statements in the background to fetch the data. If you want to, you can see the list of statements executed for each source table. In this recipe, we explore what happens under the hood when you add multiple source tables and how Data Services optimizes the extraction of the data from these source tables and even joins them together, executing complex SQL queries instead of multiple
SELECT * FROM <table>.
In this recipe, we will extract a person's name, address, and phone number from the source OLTP database and populate a new stage table PERSON_DETAILS with this data set.