Final answer:
The outer join operator is used to include all rows from one side of the two tables, even if there are no matching rows on the other side. The correct answer is 'a) LEFT JOIN' or 'b) RIGHT JOIN', depending on which side has the rows that are missing matching rows.
Step-by-step explanation:
The question refers to a type of SQL join operation. In SQL, there are different types of joins that can be used to retrieve data from multiple tables. The specific join type mentioned in the question is used when you want to include all rows from one side of the two tables being joined, even if there are no matching rows in the other table.
For the given question, the correct answer is:
- a) LEFT JOIN: This is used when you want to include all rows from the left table and the matched rows from the right table. If there is no match, NULL values are used to fill in the columns from the right table.
- b) RIGHT JOIN: This joins two tables and returns all rows from the right table, along with the matched rows from the left table. If there is no match, NULL values are used for the left table's columns.
- c) FULL JOIN: This combines the results of both LEFT and RIGHT joins. It returns all rows when there is a match in either left or right table records.
- d) INNER JOIN: This returns rows when there is at least one match in both tables.
The operator that is placed on the side that is missing the matching rows is either a LEFT JOIN or RIGHT JOIN, depending on which side of the join is considered 'deficient'. If the left side is deficient, we use a LEFT JOIN, and if the right side is deficient, we use a RIGHT JOIN.