Table of Contents for

MySQL in a Nutshell, 2nd Edition

This function returns NULL if the two arguments given are equal. Otherwise, it returns the value or results of the first argument. Here is an example:

SELECT clients.client_id AS ID,
CONCAT(name_first, SPACE(1), name_last) AS Client,
telephone_home AS Telephone,
NULLIF(
  (SELECT SUM(qty * price)
   FROM investments, stock_prices
   WHERE stock_symbol = symbol
   AND client_id = ID ), 0)
AS Value
FROM clients, investments
WHERE clients.client_id = investments.client_id
GROUP BY clients.client_id;

In this example, NULL is returned for the Value column if the value of the client’s stocks is 0 (i.e., the client had stocks but sold them all). If there is a value to the stocks, however, the sum of their values is displayed.