I am attempting to take a field and break it into two seperate fields.
Using the select statement below I am able to see it broken into two fields

select name, substring(name, 1, instr(name, ',') - 1) first, substring(name, instr(name, ',') + 1) from doctor

OUTPUT
NAME | FIRST | LAST
Doe, John | John | Doe

What I am unsure about is how to turn this into an update query to place into the appropriate fields name 'first' and 'last'

Thanks in advance.

update test a set first_name = (select substring(col_with_data,...)
from test b where <join a and b on key columns, columns that uniquely identify a row>)

and you can have the same query for last_name.

I am assuming you have blank columns already in the table.

I am not an expert, but hope this helps...

does the table actually have 3 fields for fullname, firstname, lastname?