CIS 336 STUDY Career Begins/cis336study.com CIS 336 STUDY Career Begins/cis336study.com | Page 69

( Note – EDUPE will not give this error message , however you should still follow the CORRECT procedure as discussed here to complete this problem ).

The reason for this is that you are attempting to alter data in one column that has a defined PK : FK relationship to a field in another table . Referential Integrity rules prevent this . So , how do you resolve such a problem ?

One approach to solving this dilemma is to turn off the foreign key checks that implement referential integrity rules . However , the danger here is that other users and processes operating on the database while these constraints are suspended could create or modify data in a way that compromises integrity . We can solve this second problem by preventing other users and processes from altering the data in the table in which we are working until we have turned the foreign key checks back on . We therefore need to construct a script that does the following .

a ) Locks the customer table – lock table customers write ; b ) Turns off FK checks – set foreign _ key _ checks = 0 ;

c ) Alters the table to add the auto _ increment feature to the PK field

d ) Turns FK checks back on – set foreign _ key _ checks = 1 ; e ) Unlocks the customer table – unlock tables ;