What happens if a column that is indexed contains a NULL value?
如果索引的列包含NULL值会发生什么?
2 个解决方案
#1
1
NULL behaves like any other value in SQL Server indexes. There can only be one such value in a unique index (on one column). It sorts to the beginning of the table. You can seek the index on the NULL value as well (myIndexedCol IS (NOT) NULL). And you can join on NULL using the index using more elaborate syntax.
NULL的行为与SQL Server索引中的任何其他值相似。在唯一索引中(在一列上)只能有一个这样的值。它排序到表的开头。您也可以在NULL值上查找索引(myIndexedCol IS(NOT)NULL)。并且您可以使用更精细的语法使用索引加入NULL。
#2
0
NULL MEAN NO VALUE
NULL意味着没有价值
By default, null value won't be indexed. But still I would suggest to have some filtered index like WHERE column IS NOT NULL.
默认情况下,不会为空值编制索引。但我仍然建议有一些过滤索引,如WHERE列IS NOT NULL。
#1
1
NULL behaves like any other value in SQL Server indexes. There can only be one such value in a unique index (on one column). It sorts to the beginning of the table. You can seek the index on the NULL value as well (myIndexedCol IS (NOT) NULL). And you can join on NULL using the index using more elaborate syntax.
NULL的行为与SQL Server索引中的任何其他值相似。在唯一索引中(在一列上)只能有一个这样的值。它排序到表的开头。您也可以在NULL值上查找索引(myIndexedCol IS(NOT)NULL)。并且您可以使用更精细的语法使用索引加入NULL。
#2
0
NULL MEAN NO VALUE
NULL意味着没有价值
By default, null value won't be indexed. But still I would suggest to have some filtered index like WHERE column IS NOT NULL.
默认情况下,不会为空值编制索引。但我仍然建议有一些过滤索引,如WHERE列IS NOT NULL。