IIRC the parameter order for some parameters differs between mysql_* and mysqli_* functions. But as someone else said above, built-in PDO or some other abstraction library for data access has been the way to go for more than a decade (more like closer to 20 years at least).

That said, I'm still surprised when I come in to codebases where people are still using hard-coded db function calls all over the place (mysql_* or mysqli_) I indicate that abstracting that away should be a priority. Even doing something as simple as "I want to log all the queries that I'm making for debug purposes" is essentially impossible when you have hundreds of individual calls to mysql_ embedded throughout the code. But... I've not come in to a codebase in the last... 4-5 years that does that, so either I've been lucky or that coding behavior is indeed becoming a thing of the past.