In a relational database, three basic operations, as shown in Figure 5.8, are used to develop useful sets of data: select, project, and join. The select operation creates a subset consisting of all records in the file that meet stated criteria. Select creates, in other words, a subset of rows that meet certain criteria. In our example, we want to select records (rows) from the PART table where the Part_Number equals 137 or 150. The join operation combines relational tables to provide the user with more information than is available in individual tables. In our example, we want to join the now-shortened PART table (only parts 137 or 150 will be presente) and the SUPPLER table into a single new table