SQL Server String column as a unique key

I am using a SQL se开发者_如何学编程rver table to keep related information with a URL . So there is a Column as "URL" and its type is VARCHAR . In the application we have to use this URL as a unique key to query for information (We are using something like SELECT * FROM Table WHERE URL = "www.google.com\ig")

Is there any disadvantages or known drawbacks in using a URL as a unique key?

Usually it is a better idea to have a numeric value rather than a string as a table key. See a discussion about this subject here: Database Primary Key C# mapping - String or int.

As for using a URL, it should not pose you any problem provided that you have some basic rules to avoid inserting the same (equivalent) URL twice. That is, the database will interpret "www.google.com" and "http://www.google.com" as different strings, so you should have a rule like "URLs will never have the protocol identifier" or "URLs will never end with a slash", or whatever makes sense for your design.

As the others have said - I would definitely not use a long string like an URL as the primary/clustering key on a SQL Server table - but of course, you should feel free to put a unique constraint on that column, to make sure you don't get any duplicates!

You can either do a UNIQUE CONSTRAINT or a UNIQUE INDEX - the end result is pretty much the same (the unique constraint will also be using an index behind the scenes). The plus side for a UNIQUE INDEX is that you can reference it as a foreign key in a separate table, so I almost always use that approach:

CREATE UNIQUE NONCLUSTERED INDEX UIX_YourTable_URL ON dbo.YourTable(urlField) 

If you should ever try to insert a value that's already in the table, that insert statement will be rejected with a SQL error and nothing bad can happen.

I would still create a clustered column key on the table e.g. An Auto number and then create a Unique Index on the URL column.

However I cant see why a URL is not unique and all should work as is.

You may benefit from numeric primary key if paging is needed. But still you can add numeric indexer in future. So there's no obstacle to make URL a PK.