This MySQL function returns NULL if the two arguments given are equal. Otherwise, it returns the value or results of the first argument.
Below is the syntax for this command. Text within square brackets (i.e, [ and ] ) are optional. Choices are separated by bars (i.e, | ). Ellipses preceded by a comma indicates a repeating pattern. Ellipses before or after syntax are used to highlight a relevant except from the larger syntax. Text displayed in italic letters represent text that should be replaced with the specific names related to the database (e.g., column with the name of the column).
This function returns NULL if the two arguments given are equal. Otherwise, it returns the value or results of the first argument.
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.