Erik Darling warns against using SQL_VARIANT data types:
I half-stumbled on the weirdness around SQL_VARIANT a while back while writing another post about implicit conversion. What I didn’t get into at the time is that it can give you incorrect results.
When I see people using SQL_VARIANT, it’s often in dynamic SQL, when they don’t know what someone will pass in, or what they’ll compare it to. One issue with that is you’ll have to enclose most things in single quotes, in case a string or date is passed in. Ever try to hand SQL those without quotes? Bad news bears. You don’t get very far.
Read on for the demo. I have never used SQL_VARIANT in any project. I’ve done a lot of crazy things with SQL Server (some of them intentionally) but never this.