MySQL - Many UPDATEs to run after INSERT
Let us suppose that you have built a reference data set that has two (or more) fields.  For the sake of argument lets call the table geography


Area_Code 
City


The MySQL update syntax would be

UPDATE data_table, geography
SET data_table.field2 = geography.City
WHERE data_table.field1 = geography.Area_Code


Potential pitfalls to watch out for are the data types, size and collation discrepancies between data_table.field1 and geography.Area_Code.

If geography.Area_Code is unique and must always be present make sure you stick a primary key on it.

It is probably worth  adding an index to data_table.field1.  Again, if it is mandatory and unique make it a primary key.