Why do string functions on SQL based database servers start at position 1 instead of 0?
Considering that there is no zeroeth position in a string outside of computers, shouldn't the question really be: why are strings 0-based in some of the more common programming languages? (I am not sure about the statement of "nearly every programming language" since there are many more languages than most people are aware of)

Strings in C and other languages are simply an array of characters (i.e. char[]) that are null-terminated. This is why you can reference individual characters by using the index notation (i.e. stringVariable[index]). Variables are an address to a location in memory. The index is the offset to the starting address of the array. So when thinking in terms of strings being an array, it makes sense enough to interact with them in a 0-based fashion because it is at least consistent even if sometimes a little awkward.

Why is this different in SQL? I would guess that it has to do with SQL being more about physical storage than memory allocation. While some RDBMS's do support arrays (such as PostgreSQL), that is not standard. SQL is also a high-level declarative language that hides the operational specifics of what the query engine is really doing, and so the concepts of addresses and pointers just isn't there. Hence it doesn't really make sense to think in terms of 0-based indexes when working with SQL.

As another poster notes, the source of zero-based indexing is addressing. The first address in any data block ends in zero (whether it occupies the last digit in physical memory or not). And it's not just computers - the address of the first house on your neighborhood block likely is a number like 300 - not 301.

When programming iterative functions where moduli are used (to make something happen every 5 iterations, etc.) it's handy - and faster - to work with zero-based arrays.

Please also see:


Why are zero-based arrays the norm?
Zero-based numbering