Performant Joins

The JOIN functionality in SQL-compliant databases provides a very powerful and efficient method of combining data from different sources, without the need for complicated looping structures or a series of individual SQL statements. We covered joins and join theory in detail in Chapter 2, SQL for Data Preparation.

As suggested by the name of the command, a join takes information from two or more tables and uses the contents of the records within each table to combine the two sets of information. Because we are combining this information without the use of looping structures, this can be done very efficiently. In this section, we will consider the use of joins as a more performant alternative to looping structures. The following is the Customer Information table:

Figure 6.31: Customer information

The following table shows the Order Information table:

Figure 6.32: Order information

So, with this information...