Path Expected for Join
When performing a join operation in an SQL query, you need to provide the path or condition for joining two or more tables. The path represents how the tables are related and which columns should be used to match the records.
Example 1: Inner Join
Let’s say we have two tables: “Customers” and “Orders”. The “Customers” table has a “customer_id” column, and the “Orders” table has a “customer_id” column as well to establish the relationship between them.
SELECT *
FROM Customers
INNER JOIN Orders ON Customers.customer_id = Orders.customer_id;
In this example, the path for joining the tables is defined using the “ON” keyword. We specify that the records should be matched based on the equality of the “customer_id” column in both tables. The result will be a combination of records matched from both tables.
Example 2: Left Join
The “path” can be modified depending on the join type. In a left join, all records from the left table (the one specified before the “LEFT JOIN” keyword) are included, while the matching records from the right table are added if they exist.
SELECT *
FROM Customers
LEFT JOIN Orders ON Customers.customer_id = Orders.customer_id;
In this example, the path is the same as in the previous example, but the join type is now left join. The result will include all customers, and if they have placed any orders, the order information will be displayed too. If a customer has not placed any orders, the corresponding columns from the “Orders” table will be filled with null values.
Example 3: Cross Join
A cross join generates the combination of each record from the first table with every record from the second table. No path or condition is necessary because it retrieves all possible combinations.
SELECT *
FROM Customers
CROSS JOIN Orders;
In this example, there is no path specified. The result will contain all possible combinations of customers and orders. Note that cross joins can lead to a large number of results if the tables contain a large number of records.