PostgreSQL is a popular relational database, one that was designed to be an object relational system, based on standards, and allowing for extensibility. I've always thought this was a great system, exceeding SQL Server in some ways, though falling short in others. It's popular, and certainly used enough so that Azure and Amazon Aurora include PostgreSQL compatability products.

I ran across an interesting post, where AWS has a Schema Conversion Tool that will help you migrate from Oracle to Aurora running PostgreSQL. I think this makes some sense as there are some capabilities in PostgreSQL that make moving Oracle code easy. AWS also has a Migration Service to move SQL Server to MySQL. I'm not sure how smoothly that goes, but SQL isn't a terribly complex language and perhaps the conversion isn't too bad, though I'm sure this isn't painless.

I wonder how many people will choose to move their database systems to a new platform. Whether you're on a commercial database, such as SQL Server or Oracle, or on a free one (MySQL, PostgreSQL), changing the underlying platform is disruptive for many applications. I'm sure there are some software packages that could change a driver and connection string and their code might work, but I bet that's relatively few systems.

For most of us, the cost of change is high. New skills need to be learned and new code written. Staff may leave, requiring an organization to hire new employees, which is always a bit of a gamble. The entire process is also a disruption that prevents other work from being completed in a timely manner. Often a large ROI is needed to justify the change, though that's not always the case as sometimes management decides to change for other reasons, regardless of cost, ignoring any ROI. I have even seen some developers psuh to make the platform change, working many extra hours because of some desire to port to a new platform for dubious reasons.

I do see plenty of companies looking to move away from Oracle systems, with a very large cost for support and maintenance. While SQL Server isn't always cheap, it is much less expensive and Microsoft has programs to help port Oracle to SQL Server. Companies may also choose to move to MySQL or PostgreSQL from Oracle, accepting the disruption and costs with a long view towards reducing their yearly outlay for database services.

I have migrated platforms before, and it's been an ordeal each time. I haven't ported code to a new platform, and not sure I would. Perhaps if we were abandoning a codebase and rewriting the application I'd consider it, but in most cases, the cost of staff and time to rework code makes this an expensive proposition. If you have different thoughts or experiences, let us know today.

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Although you have to write the DISTINCT before the TOP 5, SQL Server will execute the DISTINCT SORT (the SORT is implied by the ORDER BY) before limiting the results to the first 5 rows (as you can verify in the execution plan).

So the (correct) result will be 1, 2, 3, 4, 5.

It will not throw an error, since the statement uses the correct syntax (see click here )

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