The SQL EXISTS Operator
The EXISTS operator is used in a WHERE clause to check whether a subquery returns any rows.
The EXISTS operator evaluates to TRUE if the subquery returns at least one row, and FALSE otherwise.
EXISTS Syntax
SELECT column_name(s)
FROM table_name
WHERE
EXISTS (subquery);
Demo Database
Below is a selection from the "Products" table in the Northwind sample database:
| ProductID | ProductName | SupplierID | CategoryID | Unit | Price |
|---|---|---|---|---|---|
| 1 | Chais | 1 | 1 | 10 boxes x 20 bags | 18.00 |
| 2 | Chang | 1 | 1 | 24 - 12 oz bottles | 19.00 |
| 3 | Aniseed Syrup | 1 | 2 | 12 - 550 ml bottles | 10.00 |
| 4 | Chef Anton's Cajun Seasoning | 2 | 2 | 48 - 6 oz jars | 22.00 |
| 5 | Chef Anton's Gumbo Mix | 2 | 2 | 36 boxes | 21.35 |
And a selection from the "Suppliers" table:
| SupplierID | SupplierName | ContactName | Address | City | PostalCode | Country |
|---|---|---|---|---|---|---|
| 1 | Exotic Liquid | Charlotte Cooper | 49 Gilbert St. | London | EC1 4SD | UK |
| 2 | New Orleans Cajun Delights | Shelley Burke | P.O. Box 78934 | New Orleans | 70117 | USA |
| 3 | Grandma Kelly's Homestead | Regina Murphy | 707 Oxford Rd. | Ann Arbor | 48104 | USA |
| 4 | Tokyo Traders | Yoshi Nagase | 9-8 Sekimai Musashino-shi | Tokyo | 100 | Japan |
SQL EXISTS Examples
The following SQL checks if any suppliers has a product with a price lower than 10. If the subquery evaluates to TRUE; list the suppliers with a product price less than 10:
Example
SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
SELECT ProductName
FROM
Products
WHERE Products.SupplierID = Suppliers.supplierID AND Price <
10
);
The following SQL checks if any suppliers has a product with a price equal to 22. If the subquery evaluates to TRUE; list the suppliers with a product price equal to 22:
Example
SELECT SupplierName
FROM Suppliers
WHERE EXISTS (
SELECT ProductName
FROM
Products
WHERE Products.SupplierID = Suppliers.supplierID AND Price = 22
);
