How to detect compatibility errors - SQL Server 2012

Can you show the query? Just because it runs doesn't mean it's correct. :-) For example this is not legal, but it works:

SELECT CONVERT(SMALLDATETIME, modify_date) AS modify_date
FROM sys.objects AS o
ORDER BY o.modify_date;

Technically, it should be as follows, since o.modify_date is not in the SELECT list:

SELECT CONVERT(SMALLDATETIME, modify_date) AS modify_date
FROM sys.objects AS o
ORDER BY modify_date;

In this Connect bug, it was stated that this rule would be removed from the Upgrade Advisor. I suspect that one of the following (or both) happened:

1. They forgot to remove the rule as they said they would
2. They had other complications which prevented the above syntax from being blocked by the parser

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That all said, there are some breaking changes the upgrade advisor will never catch. For example, this will work on 2005, 2008 and 2008 R2:

CREATE TABLE #foo(id INT);

IF OBJECT_ID('tempdb..#foo') > 0
BEGIN
  DROP TABLE #foo;
END
GO

CREATE TABLE #foo(id INT);

This will break in SQL Server 2012, however, since #temp tables now get a negative object_id. The proper way to test is:

IF OBJECT_ID('tempdb..#foo') IS NOT NULL

I go over a few other issues in this blog post. A couple of other breaking changes:

• https://sqlblog.org/2011/06/28/sql-server-v-next-denali-breaking-change-to-fn_virtualfilestats

• https://sqlblog.org/2011/07/08/sql-server-v-next-denali-breaking-change-to-system-databases-database_id-db_id

If you use any of the memory-related DMVs there has been a major overhaul to some of the columns:

• https://blogs.msdn.microsoft.com/sqlosteam/2012/07/11/memory-manager-surface-area-changes-in-sql-server-2012/

Again, most of these are not caught by the upgrade advisor, so running that tool and not doing any thorough testing could really put you in a bad spot.

And I agree with Eric's answer - you should try to track deprecated events. For completeness, here are three approaches:

• Profiler
• Server-side trace
• Extended Events

You can also trace for deprecated calls.