When the update statement will check the constraint violation ?

Question

Hello all,
i am working on data masking of production data using oracle Translate function.i have created a function otis_mask using translate function to mask sensitive values .For this i am tesitng on a small table. i have created a table with single primary key column SSN.
sql>desc SSN_MASK
Name Null? Type
SSN NOT NULL NUMBER(10)
1) i have inserted the value 9949577766. if resulted mask value exist in table it should throw the constraint violation error.But it is not throwing any error.rows are properly updating .
Eg:-
Table contains below values.
PA_DATA_SUB @qdsrih30 >select *from SSN_MASK;
SSN
7727399911
9949577766
9989477700
UPDATE SSN_MASK SET SSN=otis_mask(SSN);
if above update statement process 7727399911 first then resulted mask value is 9989477700.This value is already in the table.
if the update statement process 9949577766 first then resulted mask value is 7727399911.This value is already in the table.
in any of the above scenario update statement should have to throw constraint violation error. But its not happening. rows are properly updating . when the update statement checking the constraint violation ? after processing all the rows or processing of each row ?
Please help me in understandding the update statement processing ?
Thanks,
Venkat Vadlamudi.

Answer 1

1)created a function as below.
CREATE OR REPLACE Function otis_mask(incol varchar2) return varchar2 is
random_str varchar2(20);
begin
select (translate(incol,'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890','qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM0842319576')) INTO random_str FROM DUAL;
return random_str;
end;
2. create a table ssn_mask.
create table ssn_mask(ssn number(10) primary key);
3) inserted 3 rows as below.
insert into ssn_mask values(9949577766);
insert into ssn_mask values(7727399911);
insert into ssn_mask values(9989477700);
4)UPDATE SSN_MASK SET SSN=otis_mask(SSN);
5) Table contains below rows.
Sql >select *from SSN_MASK;
SSN
9949577766
7727399911
9989477700.
6)UPDATE SSN_MASK SET SSN=otis_mask(SSN);
If the above statement process first row 9949577766,then otis_mask function will return 7727399911 and update statement will update the value of 9949577766 to 7727399911 .At this case 7727399911 is already in the table.So update statement should have to throw primary key constraint violation error.
If the above statement process second row 7727399911 first ,then otis_mask function will return 9989477700.and update statement will update the value of 7727399911 to 9989477700.At this case 9989477700 is already in the table.So update statement should have to throw primary key constraint violation error.
But its not throwing any integrity constraint violation error.
i just want to know when update statement will check the constraint ?
is update statement will first process all records and kepp in handy the new values then update the table with new values (or) process the first row and update the new value with old value then process second row and update with new value so on ?
Thanks,
Venkat Vadlamudi.