#!/bin/bash

echo '"2017-09-30","ACBD,TVF","01234",NULL,18,NULL,"686091802","BANK OF ABCD, LIMITED, THE",790456' | 
awk -v OFS='|' -v FPAT='"[^"]*"|[^,]*' '{
   for (h=1; h<=NF; h++) printf "%s%s", $h, (h < NF ? OFS : ORS)
}'