OR Operator Short-circuit in SQL Server

Solution 1:

Within SQL, there is no requirement that an OR clause breaks early. In other words, it is up to the optimizer whether to check both conditions simutaneously. I am not an expert in the MSSQL optimizer, but I have seen instances where the optimizer has and has not short circuited an OR clause.

Solution 2:

Just stumbled over this question, and had already found this blog-entry: http://rusanu.com/2009/09/13/on-sql-server-boolean-operator-short-circuit/

The SQL server is free to optimize a query anywhere it sees fit, so in the example given in the blog post, you cannot rely on short-circuiting.

However, a CASE is apparently documented to evaluate in the written order - check the comments of that blog post.