Oracle Internals

Chapter 32

Oracle’s Joins

Richard Earp

Sikha Bagui

There is often a need to select data from columns from more than one table. A join combines columns and data from two or more tables (and in some cases, of one table with itself). The tables are listed in a FROM clause of a SELECT statement, and a join condition between the two tables is specified in a WHERE clause.

For example, suppose we create a table called Emp with an employee number (Empno) and a job code (JobCode) as follows:

   Emp
   Empno   JobCode
   101     cp
   102     ac
   103     de

And then we create a second table called Job, which contains the job code (JobC) and a job title (JobTitle):

  Job
  JobC   JobTitle
  de     dentist
  ac     accountant
  do     doctor

We can use the following join command:

 SELECT * ...