Coalesce (MS SQL Server)——取指定內容（列）中第一個不為空的值
oalesce 獲得引數中第一個不為空的表示式。
語法：
COALESCE ( expression [ ,...n ] )
例子：
CREATE TABLE wages /*建立表wages*/
(
emp_id tinyint identity,
hourly_wage decimal NULL,
salary decimal NULL,
commission decimal NULL,
num_sales tinyint NULL
)
GO
INSERT wages VALUES(10.00, NULL, NULL, NULL) /*插入值*/
INSERT wages VALUES(20.00, NULL, NULL, NULL)
INSERT wages VALUES(30.00, NULL, NULL, NULL)
INSERT wages VALUES(40.00, NULL, NULL, NULL)
INSERT wages VALUES(NULL, 10000.00, NULL, NULL)
INSERT wages VALUES(NULL, 20000.00, NULL, NULL)
INSERT wages VALUES(NULL, 30000.00, NULL, NULL)
INSERT wages VALUES(NULL, 40000.00, NULL, NULL)
INSERT wages VALUES(NULL, NULL, 15000, 3)
INSERT wages VALUES(NULL, NULL, 25000, 2)
INSERT wages VALUES(NULL, NULL, 20000, 6)
INSERT wages VALUES(NULL, NULL, 14000, 4)
GO
SET NOCOUNT OFF
GO
SELECT CAST(COALESCE(hourly_wage * 40 * 52, /*取hourly_wage*40*52和salary列中不為空的列的值*/
salary,
commission * num_sales) AS money) AS 'Total Salary'
FROM wages
GO
Here is the result set:
Total Salary ------------ 20800.0000 41600.0000 62400.0000 83200.0000 10000.0000 20000.0000 30000.0000 40000.0000 45000.0000 50000.0000 120000.0000 56000.0000 (12 row(s) affected)