What is a NULL Value? A field with a NULL value is a field with no value. If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field. Then, the field will be saved with a NULL value.

The SQL Server ISNULL() function lets you return an alternative value when an expression is NULL: SELECT ProductName, UnitPrice * (UnitsInStock + ISNULL(UnitsOnOrder, 0)) FROM Products;

The IS NOT NULL Operator. The IS NOT NULL operator is used to test for non-empty values (NOT NULL values). The following SQL lists all customers with a value in the "Address" field:

If there is no ELSE part and no conditions are true, it returns NULL. CASE Syntax

The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.

Here we use the COUNT() function and the GROUP BY clause, to return the number of records for each category in the Products table: Example SELECT COUNT(*) AS [Number of records], CategoryID

SQL is a standard language for storing, manipulating and retrieving data in databases. Our SQL tutorial will teach you how to use SQL in: MySQL, SQL Server, MS Access, Oracle, Sybase, Informix, Postgres, and other database systems.

SQL Statement: SELECT CustomerName, ContactName, Address FROM Customers WHERE Address IS NOT NULL; Edit the SQL Statement, and click "Run SQL" to see the result.

The SQL WHERE Clause. The WHERE clause is used to filter records. It is used to extract only those records that fulfill a specified condition.

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