用 COALESCE 函数来替代一长串的 CASE WHEN ... ELSE 语句(T-SQL)
(COALESCE function instead of long CASE WHEN ... ELSE (T-SQL))
当你希望找出一个不为NULL的值时, 你可以使用 COALESCE 函数, 而不是使用一长串 "SELECT ... CASE WHEN ... ELSE ..." construction, . 让我们来看看下面这段 T-SQL 语句, 其中我们希望找出一个有效的(available) "source":
SELECT TheSource =
CASE
WHEN localSource IS NOT NULL THEN localSource
WHEN intranetSource IS NOT NULL THEN intranetSource
WHEN internetSource IS NOT NULL THEN internetSource
ELSE ''
END
FROM ...
现在我们用 COALESCE 函数来重写上面这段代码:
SELECT TheSource =
COALESCE(localSource, intranetSource, internetSource, '')
FROM ...
这条提示适用于MS SQL Server 2000/2005.
1/15/2008