Oracle Exam 1Z0-071 Topic 13 Question 113 Discussion

In Oracle SQL, when performing a JOIN operation, the ON clause is used to specify the condition that relates the two tables being joined. The WHERE clause can be used to further filter the result set.

A) This is a valid join condition using the WHERE clause to filter the rows after the join has been made.

B) This statement will fail because the ON clause should only contain conditions that relate the two tables. The condition for filtering the departments table should be in the WHERE clause, not in the ON clause. This is a common mistake when writing JOIN statements.

C) This is a correct statement. The ON clause specifies how the tables are related and the WHERE clause specifies an additional filtering condition for the query.

D) This statement is also correct. It's similar to the first statement (A) and properly places the department_id filter in the ON clause, which is acceptable though not typically best practice as it can be less readable than using a WHERE clause for non-join conditions.

When the JOIN operation is executed, the database first pairs rows from the joined tables that meet the join condition specified by the ON clause. Then, it filters the result of the JOIN operation based on the condition specified in the WHERE clause.

Oracle Documentation on Joins: https://docs.oracle.com/database/121/SQLRF/queries006.htm#SQLRF52359