Question

我有以下格言:

select s.comments + s.further_comments from dbo.samples s where id = 1234

However if s.comments or s.further_comments is NULL the whole string is returned NULL

我如何将民族解放军的价值转化为空洞的扼杀,或至少只把非民族解放军的价值观归为这种扼杀?

Answer 1

http://msdn.microsoft.com/en-us/library/a933210%28v=sql.80%29.aspx”rel=“nofollow”

SELECT ISNULL(s.comments,   ) + ISNULL(s.further_comments,   )
SELECT COALESCE(s.comments,   ) + COALESCE(s.further_comments,   )

http://msdn.microsoft.com/en-us/library/a2582 4428v=sql.80%29.aspx”rel=“nofollow”

Replaces NULL with the specified replacement value.

http://msdn.microsoft.com/en-us/library/a2582 4428v=sql.80%29.aspx“rel=” COALESCE。

Returns the first nonnull expression among its arguments.

请注意,are,在这两种方法之间,但就所有意图和目的而言,最有可能不适用于你的情况。

ISNULL(NULL, NULL) -- is int

COALESCE(NULL, NULL) -- Will throw an error

COALESCE(CAST(NULL as int), NULL) -- it valid and returns int

ISNULL takes only 2 parameters whereas COALESCE takes variable number of parameters

COALESCE is based on the ANSI SQL standard whereas ISNULL is a proprietary TSQL function

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