Note

Functions Are Less Portable Than SQL Code that runs on multiple systems is said to be portable. Most SQL statements are relatively portable, and when differences between SQL implementations do occur they are usually not that difficult to deal with. Functions, on the other hand, tend to be far less portable. Just about every major Database Management System (DBMS) supports functions that others don't, and sometimes the differences are significant.

With code portability in mind, many SQL programmers opt not to use any implementation-specific features. Although this is a somewhat noble and idealistic view, it is not always in the best interests of application performance. If you opt not to use these functions, you make your application code work harder. It must use other methods to do what the DBMS could have done more efficiently.

If you do decide to use functions, make sure you comment your code well, so that at a later date you (or another developer) will know exactly to which SQL implementation you were writing.