hello,
i have two standard object Account(parent) and Contact(child) .so i wanna create a custom field  'sequence number' on Contact .
suppose my Account(parent) Object have 5 Contact(child) the 'sequence number' record is 1,2,3,4,5      Than i will delete the One 'sequence number' record 3  so my 4 number come to 3  and 5 number is come to 4.    the new 'sequence number' is 1,2,3,4  
if i will delete any record than the sequence of record number is maintan.
this is done help by 'Apex Trigger'.
help my and example with code