SQL is null function

Sql ISNULL() 函数 使用指定的替换值替换 NULL。语法ISNULL( check_expression , replacement_value ) 参数check_expression将被检查是否为 NULL的表达式。check_expression 可以是任何类型的。replacement_value 在 check_expression 为 NULL时将返回的表达式。replacement_value 必须与 check_expresssion 具有相同的类型。返回类型返回与 check_expression 相同的类型。注释如果 check_expression 不为 NULL，那么返回该表达式的值；否则返回 replacement_value。示例A. 将 ISNULL与 AVG一起使用下面的示例查找所有书的平均价格，用值 $10.00 替换 titles 表的 price 列中的所有 NULL条目。USE pubsGOSELECTAVG(ISNULL(price, $10.00))FROMtitlesGO下面是结果集：-------------------------- 14.24                         (1 row(s) affected)B. 使用 ISNULL下面的示例为 titles 表中的所有书选择书名、类型及价格。如果一个书名的价格是 NULL，那么在结果集中显示的价格为 0.00。USE pubsGOSELECTSUBSTRING(title, 1, 15) AS Title, type ASType,       ISNULL(price, 0.00) ASPriceFROMtitlesGO下面是结果集：Title              Type            Price             --------------- ------------ -------------------------- The Busy Execut business        19.99                         Cooking withCo business        11.95                         You Can Combat     business        2.99                          Straight Talk A business        19.99                         Silicon Valley     mod_cook        19.99                         The Gourmet Mic mod_cook        2.99                          The Psychology     UNDECIDED       0.00                          But IsIt User popular_comp 22.95                         Secrets ofSili popular_comp 20.00                         Net Etiquette      popular_comp 0.00                          Computer Phobic psychology      21.59                         IsAnger the En psychology      10.95                         Life Without Fe psychology      7.00                          Prolonged Data     psychology      19.99                         Emotional Secur psychology      7.99                          Onions, Leeks,     trad_cook       20.95                         Fifty Years in trad_cook       11.95                         Sushi, Anyone?     trad_cook       14.99                         (18 row(s) affected)

SQL is null function