SQL & PL/SQL

Hi,

Apologies for how basic this query will likely be, but I'm teaching myself from scratch and don't like to move from topic to topic without a good understanding of why I'm getting the results I'm getting, rather than just knowing 'that's the way it's done'.

I'm using the official exam guide for 1z0-051, and on page 320 there is the following exercise:

+"The JOB_HISTORY table shares three identically named columns with the EMPLOYEES table: EMPLOYEE_ID, JOB_ID, and DEPARTMENT_ID. You are required to describe the tables and fetch the EMPLOYEE_ID, JOB_ID,+
+DEPARTMENT_ID, LAST_NAME, HIRE_DATE, and END_DATE values for all rows retrieved using a pure natural join. Alias the EMPLOYEES table as EMP and the JOB_HISTORY table as JH and use dot notation where possible."+


Their solution to this (which is pretty much what I initially came up with) is:

SELECT employee_id, job_id, department_id, emp.last_name, emp.hire_date, JH.end_date
FROM job_history JH
NATURAL JOIN employees emp;

This results in the single employee 'Taylor' being returned.

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Is there any chance someone could 'hold my hand' through this example please? I have no idea why only one result is returned, but additionally I don't know what else I was expecting - clearly my understanding of the natural join clause is severely lacking. The book states that:

+"Executing this statement returns a single row with the same EMPLOYEE_ID, JOB_ID, and DEPARTMENT_ID values in both tables"+

I guess I'm confused because I thought that the join clauses were to enable additional content from other tables to be displayed, not to limit the rows - which is what it sounds like they mean by "returns a single row with the same employee_id, job_id, and department_id values in both tables".



I'm very confused!!!

Thanks in advance,

Nick