>>STREXTRACT() would require special case handling for the first pair, wouldn't it? It has no way to select a partial string unless it begins with a delimiter - or am I missing something?

yourstring="123,456,abc"
STREXTRACT( yourstring, "", ",")

will extract "123", the first field

yourstring="123,456,abc"
STREXTRACT( yourstring, ",", "")

will extract "abc", the last field, in the above example