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steave
answered Apr 24 '23 00:00
The WHERE clause filters rows from a result set after a JOIN operation has been performed. It applies to the result set of the JOIN and can reference columns from any table in the JOIN. Typically, the WHERE clause is used to impose additional conditions beyond the join conditions.
For instance, consider the query below that joins two tables, orders and customers , using the customer_id column:
SELECT *
FROM orders
JOIN customers ON orders.customer_id = customers.customer_id
WHERE orders.status = 'shipped'
In this query, the join condition is specified in the ON clause, which states that the customer_id column in the orders table must match the customer_id column in the customers table. The WHERE clause is then used to further filter the result set by specifying that only orders with a status of 'shipped' should be included.
The ON clause, on the other hand, is used to specify the join condition between two tables. It joins rows from two tables based on a common column or set of columns. The ON clause is typically used in INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN statements.
For example, consider the query below that joins two tables, orders and customers , using the customer_id column:
SELECT *
FROM orders
JOIN customers ON orders.customer_id = customers.customer_id
In this query, the join condition is specified in the ON clause, which states that the customer_id column in the orders table must match the customer_id column in the customers table. The result set will include all rows from both tables where the join condition is true.
To summarize, the WHERE clause filters the result set after a JOIN operation, while the ON clause specifies the join condition between two tables.