Advantages of SQL Server 2008 over SQL Server 2005?

• Transparent Data Encryption. The ability to encrypt an entire database.
• Backup Encryption. Executed at backup time to prevent tampering.
• External Key Management. Storing Keys separate from the data.
• Auditing. Monitoring of data access.
• Data Compression. Fact Table size reduction and improved performance.
• Resource Governor. Restrict users or groups from consuming high levels or resources.
• Hot Plug CPU. Add CPUs on the fly.
• Performance Studio. Collection of performance monitoring tools.
• Installation improvements. Disk images and service pack uninstall options.
• Dynamic Development. New ADO and Visual Studio options as well as Dot Net 3.
• Entity Data Services. Line Of Business (LOB) framework and Entity Query Language (eSQL)
• LINQ. Development query language for access multiple types of data such as SQL and XML.
• Data Synchronizing. Development of frequently disconnected applications.
• Large UDT. No size restriction on UDT.
• Dates and Times. New data types: Date, Time, Date Time Offset.
• File Stream. New data type VarBinary(Max) FileStream for managing binary data.
• Table Value Parameters. The ability to pass an entire table to a stored procedure.
• Spatial Data. Data type for storing Latitude, Longitude, and GPS entries.
• Full Text Search. Native Indexes, thesaurus as metadata, and backup ability.
• SQL Server Integration Service. Improved multiprocessor support and faster lookups.
• MERGE. TSQL command combining Insert, Update, and Delete.
• SQL Server Analysis Server. Stack improvements, faster block computations.
• SQL Server Reporting Server. Improved memory management and better rendering.
• Microsoft Office 2007. Use OFFICE as an SSRS template. SSRS to WORD.
• SQL 2000 Support Ends. Mainstream Support for SQL 2000 is coming to an end.

(Good intro article part 1, part 2, part 3. As for compelling reasons, that depends on what you are using SQL server for. Do you need hierarchical data types? Do you currently store files in the database and want to switch over to SQL Server's new filestream feature? Could you use more disk space by turning on data compression?

And let's not forget the ability to MERGE data.

Be aware that a lot of the really killer features are only in Enterprise Edition. Data compression and backup compression are among two of my top favorites - they give you free performance improvements right off the bat. Data compression lessens the amount of I/O you have to do, so a lot of queries speed up 20-40%. CPU use goes up, but in today's multi-core environments, we often have more CPU power but not more IO. Anyway, those are only in Enterprise.

If you're only going to use Standard Edition, then most of the improvements require changes to your application code and T-SQL code, so it's not quite as easy of a sell.

Someone with more reputation can copy this into the main answer:

• Change Tracking. Allows you to get info on what changes happened to which rows since a specific version.
• Change Data Capture. Allows all changes to be captured and queried. (Enterprise)

I guess it depends on your role

For me as a developer:

• Merge statement
• Reporting Services improvement
• Date/time changes

Edit, late update, after using it

• filtered indexes
• table valued parameters
• Reporting Services without IIS

I went to a bunch of SQL Server 2008 talks in PASS 2008, the only 'killer feature' from my point of view is extended events.

There are lots of great improvements, but that was the only one that got close to being a game changer for me. Table value parameters and merge were probably my next favourite. Day-to-day, IntelliSense is a huge win.. But this isn't really specific to SQL Server 2008, just the SQL Server 2008 toolset (other tools can give you similar IntelliSense against SQL Server 2005, 2000, etc.).

There are new features added. But, you will have to see if it is worth the upgrade. Some good improvements in Management Studio 2008 though, especially the intellisense for the Query Editor.

SQL 2008 also allows you to disable lock escalation on specific tables. I have found this very useful on small frequently updated tables where locks can escalate causing concurrency issues. In SQL 2005, even with the ROWLOCK hint on delete statements locks can be escalated which can lead to deadlocks. In my testing, an application which I have developed had concurrency issues during small table manipulation due to lock escalation on SQL 2005. In SQL 2008 this problem went away.

It is still important to bear in mind the potential overhead of handling large numbers of row locks, but having the option to stop escalation when you want to is very useful.

One of my favourites are Filtered indexes. Now I can create lightning fast covering indexes for my most critical queries with only minor impact on DML statements.

/Håkan Winther

SQL Server 2008 introduces four new date and time data types, which include:

* DATE: As you can imagine, the DATE data type only stores a date in the format of YYYY-MM-DD. It has a range of 0001-01-01 through 9999-12-32, which should be adequate for most business and scientific applications. The accuracy is 1 day, and it only takes 3 bytes to store the date.
* TIME: TIME is stored in the format: hh:mm:ss.nnnnnnn, with a range of 00:00:00.0000000 through 23:59:59:9999999 and is accurate to 100 nanoseconds. Storage depends on the precision and scale selected, and runs from 3 to 5 bytes.
* DATETIME2: DATETIME2 is very similar to the older DATETIME data type, but has a greater range and precision. The format is YYYY-MM-DD hh:mm:ss:nnnnnnnm with a range of 0001-01-01 00:00:00.0000000 through 9999-12-31 23:59:59.9999999, and an accuracy of 100 nanoseconds. Storage depends on the precision and scale selected, and runs from 6 to 8 bytes.
* DATETIMEOFFSET: DATETIMEOFFSET is similar to DATETIME2, but includes additional information to track the time zone. The format is YYYY-MM-DD hh:mm:ss[.nnnnnnn] [+|-]hh:mm with a range of 0001-01-01 00:00:00.0000000 through 0001-01-01 00:00:00.0000000 through 9999-12-31 23:59:59.9999999 (in UTC), and an accuracy of 100 nanoseconds. Storage depends on the precision and scale selected, and runs from 8 to 10 bytes.

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