sql - 对表中的列强制执行唯一和多个NULL

Question

如何在SQL Server中为表的列强制执行Unique值以及多个NULL？

Answer 1

从this answer:

In SQL Server 2008, you can define a unique filtered index based on a predicate that excludes NULLs:

CREATE UNIQUE NONCLUSTERED INDEX idx_yourcolumn_notnull
ON YourTable(yourcolumn)
WHERE yourcolumn IS NOT NULL;

In earlier versions, you can resort to VIEWS with a NOT NULL predicate to enforce the constraint.