Auto generated SQL Server keys with the uniqueidentifier or IDENTITY
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Note: your email address is not published. Monday, April 02, 2012 - 1:37:32 AM - Enigmatic One thing that wasn't listed were the disadvantages of using IDENTITY columns. In terms of query performance rather than write performance , you might want to use a column that is frequently used in ORDER BY, GROUP BY, JOINS foreign keys or where the column is often used to select a range of values etc. NEWID randomly generates a guaranteed unique value based on the identification number of the server's network card plus a unique number from the CPU clock.
As a result, they don't suffer from the page splitting condition that plagues the NEWID approach. You can choose any other column as the clustered index, then the data rows will be physically ordered by that column.
Create Table with Primary Key autoincrement - Probably they thought using GUIDs is cheaper than doing key fix ups?
Much to the frustration of database administrators worldwide, prior to Oracle version 12c in mid-2014, Oracle simply had no inherent ability to inherently generate auto incrementing columns within a table schema. While the reasons for this design decision can only be guessed at, the good news is that even for users on older Oracle systems, there is a possible workaround to circumnavigate this pitfall and create your own auto incremented primary key column. Creating a Sequence The first step is to create a in your database, which is a data object that multiple users can access to automatically generate incremented values. This is where come in. Similar to an event in modern programming languages, a TRIGGER in Oracle is a stored procedure that is executed when a particular event occurs. Typically a TRIGGER will be configured to fire when a table is updated or a record is deleted, providing a bit of cleanup when necessary. In our case, we want to execute our TRIGGER prior to INSERT into our books table, ensuring our SEQUENCE is incremented and that new value is passed onto our primary key column. Note: The FROM dual part is necessary to complete a proper query but is effectively irrelevant. The dual table is just a single dummy row of data and is added, in this case, just so it can be ignored and we can instead execute the system function of our trigger rather than returning data of some kind. IDENTITY Columns columns were introduced in Oracle 12c, allowing for simple auto increment functionality in modern versions of Oracle. Using the IDENTITY column is functionally similar to that of other database systems.
If there will frequent access of a customer table by territory number, it may be best to set up a clustered index by that column. In this situation GUIDs would probably be the most attractive option IMO. You would need to export all the data out then you can change column type to IDENTITY or vice versa and then import data back. Though you can defragment the NEWID table, the random nature of the key generation will still cause page splitting and fragmentation with all future table INSERTs. All comments are reviewed, so stay on subject or we may delete your comment. Its silly for Microsoft to have left the clustered index on an identity or guid column for that matter.
