sql-server - T-SQL : What does this passage in the COALESCE documentation mean?

Question

ISNULL and COALESCE though equivalent, can behave differently. An expression involving ISNULL with non-null parameters is considered to be NOT NULL, while expressions involving COALESCE with non-null parameters is considered to be NULL.

http://msdn.microsoft.com/en-us/library/ms190349.aspx

Answer 1

它确定使用 ISNULL 或 COALESCE 的计算列的可为空性

RowCheckSum AS COALESCE(...)

...意味着 RowCheckSum 列定义具有 NULL 关键字，并且

RowCheckSum2 AS ISNULL(...)

...具有 NOT NULL 定义。

这也意味着，在结果集中，第一个字段可以返回 NULL 值，而第二个字段则不能。