Question

When no join type between multiple tables in a query's FROM clause is specified, what type of join is assumed?

a) INNER JOIN
b) LEFT JOIN
c) RIGHT JOIN
d) CROSS JOIN

Answer 1

When the join type is not specified between multiple tables in a SQL query's FROM clause, an INNER JOIN is assumed. This join returns rows with at least one match in both tables, and other join types must be explicitly stated to be utilized.

Step-by-step explanation:

When a join type is not explicitly specified between multiple tables in a query's FROM clause, the type of join that is assumed is an INNER JOIN. This default behavior is observed in most relational database management systems (RDBMS) such as MySQL, PostgreSQL, and SQL Server. An INNER JOIN returns rows when there is at least one match in both tables involved in the join. It is important to note that other types of joins, like LEFT JOIN, RIGHT JOIN, or CROSS JOIN, must be explicitly stated to be used.

Here's an example for clarity: Suppose we have two tables, Customers and Orders. If we want to retrieve all orders made by customers, we could write a query using an implicit INNER JOIN like this:

SELECT *
FROM Customers, Orders
WHERE Customers.CustomerID = Orders.CustomerID;

In this scenario, the query will return all orders along with their respective customer information only if a matching record exists in both tables.