Uniqueness And Multiple NULL Values

Dennes Torres shows how to allow an indefinite number of NULL values  while guaranteeing non-NULL values are unique:

Regardless of using unique constraint or unique index, the field can accept null values, however the uniqueness will result in only accepting a single row with null value.

The solution to allow nulls in unique fields is create a unique filtered index excluding the nulls of the index, due to that the uniqueness of the nulls will not be validated and multiple rows with nulls will be accepted.

Click through for the code.  I enjoy asking this as an interview question.  It’s a non-trivial problem with a non-trivial solution and isn’t a trick question.

Related Posts

Filtered Index Trickiness

Greg Low explains some of the tricky bits behind using filtered indexes: If you think about it, if all we’re ever going to use is one part of the index, i.e. just the unfinalized rows, having an entry in there for every single row is quite wasteful, as although the vast majority of the index […]

Read More

Creating Cosmos DB Indexes

Hasan Savran explains indexing in Cosmos DB: In SQL Server you need to pick which columns you like to index, In CosmosDB you need to pick which columns not to index. It’s kind of same thing at the end. You might ask “If everything is indexed and working fine, why do you want me to […]

Read More

Categories

December 2016
MTWTFSS
« Nov Jan »
 1234
567891011
12131415161718
19202122232425
262728293031