SQL: WHERE Clause

The WHERE clause allows you to filter the results from an SQL statement - select, insert, update, or delete statement.

It is difficult to explain the basic syntax for the WHERE clause, so instead, we'll take a look at some examples.

Example #1

SELECT *
FROM suppliers
WHERE supplier_name = 'IBM';

In this first example, we've used the WHERE clause to filter our results from the suppliers table. The SQL statement above would return all rows from the suppliers table where the supplier_name is IBM. Because the * is used in the select, all fields from the suppliers table would appear in the result set.

Example #2

SELECT supplier_id
FROM suppliers
WHERE supplier_name = 'IBM'
or supplier_city = 'Newark';

We can define a WHERE clause with multiple conditions. This SQL statement would return all supplier_id values where the supplier_name is IBM or the supplier_city is Newark.

Example #3

SELECT suppliers.suppler_name, orders.order_id
FROM suppliers, orders
WHERE suppliers.supplier_id = orders.supplier_id
and suppliers.supplier_city = 'Atlantic City';

We can also use the WHERE clause to join multiple tables together in a single SQL statement. This SQL statement would return all supplier names and order_ids where there is a matching record in the suppliers and orders tables based on supplier_id, and where the supplier_city is Atlantic City.