stored procedure with dual personality

[rich300]

I have a long, complicated set of conditions that I would like to use in a MySQL stored procedure to either (a) update a table with the complicated set of conditions in the WHERE clause, or (b) return a single value based on the same set of complicated conditions. I know how to write a stored procedure to do one or the other, but cannot see a way to have one stored procedure, an input parameter to say whether the output will be A or B, and without duplicating the complicated conditions. I am stuck at seeing that A needs an Update statement, and B needs an if-then statement, and both need the same complicated conditions inside the respective statements.

I should add that the complicated conditions are based on the content of other fields in each record. So for option B it is a simple matter of looking at the other parameters for a single case. But for option A, there is a whole table of records that need to be updated where the output for each record depends on the contents of other fields in that record.