In SQL, the EXISTS operator is used to check the existence of rows in a subquery. It returns true if the subquery returns any rows, and false otherwise. The EXISTS operator is often used in combination with a correlated subquery to perform conditional queries. The syntax for using EXISTS is as follows:

sql
SELECT column1, column2, ...
FROM table
WHERE EXISTS (subquery);

In this syntax:

- `column1`, `column2`, etc. are the columns you want to retrieve from the table.
- `table` is the name of the table you are querying.
- `subquery` is a separate query that returns rows to be evaluated by the EXISTS operator. This subquery can include conditions and references to the outer query.

Here's an example to illustrate the usage of EXISTS:

sql
SELECT product_name
FROM products
WHERE EXISTS (
    SELECT 1
    FROM orders
    WHERE orders.product_id = products.product_id
    AND orders.order_date >= '2022-01-01'
);

In this example, the query retrieves the product names from the "products" table for products that have orders placed after January 1, 2022. The EXISTS operator is used in the WHERE clause with a correlated subquery. The subquery checks if there are any rows in the "orders" table where the product_id matches the current product from the outer query and the order_date is greater than or equal to January 1, 2022.

The EXISTS operator is useful when you want to filter rows based on the existence of related rows in another table or the result of a subquery. It allows you to perform conditional queries and make decisions based on the presence or absence of certain data in the subquery.