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How to Use the Join Operator In Oracle Sql?

3 minutes read

In Oracle SQL, the JOIN operator is used to combine rows from two or more tables based on a related column between them. This related column is typically a primary key in one table and a foreign key in another table.


There are different types of JOINs such as INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN. INNER JOIN returns only the rows that have matching values in both tables, while LEFT JOIN returns all the rows from the left table and the matched rows from the right table. RIGHT JOIN does the opposite of the LEFT JOIN, returning all the rows from the right table and the matched rows from the left table. FULL JOIN returns all the rows when there is a match in either table.


The syntax for using the JOIN operator in Oracle SQL is as follows:


SELECT columns FROM table1 JOIN table2 ON table1.column_name = table2.column_name;


This statement selects columns from table1 and table2 where the values in column_name are equal in both tables. The JOIN condition is specified using the ON keyword.


Overall, the JOIN operator is a powerful tool in Oracle SQL that allows you to retrieve data from multiple tables based on a common column.


What is the result of a left outer join in Oracle SQL?

A left outer join in Oracle SQL returns all records from the left table (the first table mentioned in the SQL query) and the matched records from the right table. If no matches are found, NULL values are returned for the columns from the right table.


What is the result of a full outer join in Oracle SQL?

A full outer join in Oracle SQL will return all records when there is a match in either the left or right table, and NULL values for any unmatched records in the corresponding table. This means that the result set will include all records from both tables, with NULL values filled in for any missing matches.


What is the purpose of a self join in Oracle SQL?

The purpose of a self join in Oracle SQL is to join a table with itself. This can be useful in scenarios where you want to compare rows within the same table or retrieve related data from the same table. It allows you to query and retrieve data based on relationships or comparisons within the same dataset. Self joins can be particularly helpful in hierarchical structures or when you need to compare data within a single table.


How to perform a right outer join using the join operator in Oracle SQL?

To perform a right outer join using the join operator in Oracle SQL, you can use the following syntax:

1
2
3

SELECT column1, column2, ...
FROM table1
RIGHT OUTER JOIN table2 ON table1.column_name = table2.column_name;


In this syntax:

  • table1 and table2 are the names of the tables you are joining.
  • column1, column2, ... are the columns you want to select from the tables.
  • table1.column_name = table2.column_name is the condition used to join the tables.


The RIGHT OUTER JOIN keyword specifies that all rows from the right table (table2) should be returned, along with matching rows from the left table (table1) if there are any.


You can also use the shorthand RIGHT JOIN instead of RIGHT OUTER JOIN, as they are equivalent.

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