A join operation allows you to retrieve data from multiple tables in a single SELECT query. Two tables can be joined by a single join operator, but the result can be joined again with other tables. There must exist a same or similar column between the tables being joined.
When you design an entire database system using good design principles like
normalization
, we often require the use of joins to give a complete picture to a user's query. For example, we split our programming languages table into two in Chapter 7 – one holding the author details (Table 11-2) and the other holding information about ...
