What is self join explain with example?

A self-join is a join that can be used to join a table with itself. Hence, it is a unary relation. In a self-join, each row of the table is joined with itself and all the other rows of the same table. Thus, a self-join is mainly used to combine and compare the rows of the same table in the database.

Where is self join used?

5 Answers. You use a self join when a table references data in itself. E.g., an Employee table may have a SupervisorID column that points to the employee that is the boss of the current employee. It’s basically used where there is any relationship between rows stored in the same table.

What do you mean by self join?

SELF JOIN: As the name signifies, in SELF JOIN a table is joined to itself. That is, each row of the table is joined with itself and all other rows depending on some conditions. In other words we can say that it is a join between two copies of the same table.

What is self join and how it works?

A self join is a join in which a table is joined with itself (which is also called Unary relationships), especially when the table has a FOREIGN KEY which references its own PRIMARY KEY. To join a table itself means that each row of the table is combined with itself and with every other row of the table.

What is the purpose of a self join?

A self join is a join that joins a table with itself. A self join is useful for comparing rows within a table or querying hierarchical data. A self join uses other joins such as inner join and left join.

Which is the simplest join left or right?

The simplest Join is INNER JOIN. INNER JOIN: The INNER JOIN keyword selects all rows from both the tables as long as the condition satisfies. LEFT JOIN: This join returns all the rows of the table on the left side of the join and matching rows for the table on the right side of join. RIGHT JOIN: RIGHT JOIN is similar to LEFT JOIN.

Which is an example of self join in SQL?

Examples to Implement in SQL Self Join. Here are a few examples to illustrate self joins in SQL. Example #1. Find the pairs of customers who belong to the same city. Code: SELECT t1.Customer AS Customer1, t2.Customer AS Customer2, t1.City FROM Customers t1, Customers t2 WHERE t1.ID <> t2.ID AND t1.City = t2.City ORDER BY t1.City;

How does the right join work in SQL?

The SQL RIGHT JOIN returns all rows from the right table, even if there are no matches in the left table. This means that if the ON clause matches 0 (zero) records in the left table; the join will still return a row in the result, but with NULL in each column from the left table.