![]() ![]() Id UNIQUEIDENTIFIER PRIMARY KEY default NEWID(), To set a default value for the column we will use the default keyword and set the default value as the value returned by the NEWID() function: Here's a statement for creating a table with the UNIQUEIDENTIFIER data type. How you create a GUID varies across different databases, but, in SQL Server, the NEWID() function is used as shown below: ![]() Short for "Globally Unique IDentifier", GUID is a 16 byte binary data type that is guaranteed to be unique across tables, databases, and even servers. One way around this problem is to use GUIDs. If you have more than one database, auto-incrementing keys can cause redundant records. ![]() And there are an endless number of other examples, such as vehicle VIN numbers, invoice IDs, etc. Also, countries have alphabetic ISO codes. For example, US states have an alphabetic code which is unique and is meaningful as a key outside the schema. Performance may be hampered slightly, but it's slightly less important than correctness, integrity, and appropriate modelling, in the estimation of many database developers.Ī non-obvious benefit of alphabetic keys is that a short symbolic string can simplify debugging by being immediately human-readable in data dumps (without additional joins). If so, then adding an artificial key just for the sake of an integer type adds nothing but redundancy. There is often a sensible natural primary key for your data which has a universal meaning and may not be an integer. Now it's time to set the record straight and conclude whether or not string - or alphabetic - data can make a suitable PK. Part 2 explored String and Numeric data types as Primary Keys in an effort to ascertain whether one is preferable to the other. Recall that, in Part 1, we covered Natural and Surrogate Primary Keys and considered why one might choose one over the other. In this third and final installment of this series on choosing a Primary Key for relational databases we'll be examining some of the reasons for employing string data as a Primary Key (PK). Choosing a Primary Key - Part 3 by Robert Gravelle Strings as Primary Keys ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |