Problem solving questions are good, but sometimes a couple of simple technical questions are enough to weed people out.

I asked a candidate what versions of SQL Server they had worked with and they told me "SQL Server 2010 and before that SQL Server 2003". That was enough to let me know that their SQL Server experience had to have been very light.

I like to ask some technical questions about things that I think anyone with good experience should know, before I get into more challenging things, like asking how they would troubleshoot a system slowdown. There have been plenty that didn't get past the simple technical questions.

For example, if I ask someone how to add three hours to a datetime and I don't get something with DATEADD, I know they have limited TSQL programming experience.