Oracle check constraint1 [closed] - sql

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I have a column Hire_date in table x with data
01-jun-98
16-aug-99
02-feb-09
01-mar-06
-
01-dec-08
17-mar-99
16-feb-07
I was asked to create a check constraint on that Hire_date column. Check that the hire_date comes after 2000. I see an error
I tried again to check if the hire_date comes after 1996. The constraint was successfully created.
why did i see an error when i created a check constraint for hire_date>2000 ?
Code:
alter table x
add constraint check_hire_date check(hire_Date>'01-jan-2000')
got error
alter table x
add constraint check_hire_date check(hire_Date>'01-jan-1996')
successful

Answer 1

The reason you got error is obvious. Some of your data violate the constraint. When you add a constraint to a table, it will validate the all data to the constraint.
You can use novalidate option to skip the validation. If you apply novalidate option when you create the constraint, you can add the constraint while you don't validate the old(=current) date with the constraint. The constraint will affect to the data which is inserted after the creation of the constraint.
sql> create table x (hire_date date);
sql> insert into x values ('1998-01-01');
sql> insert into x values ('2000-01-05');
sql> select * from x;
HIRE_DAT
--------
98/01/01
00/01/05
sql> alter table x add constraint d_check check
2 (hire_date >= to_date('2000-01-01', 'yyyy-mm-dd'))
3 novalidate;
sql> insert into x values ('1999-01-01');
insert into x values ('1999-01-01')
*
error at line 1:
check constraint (d_check check) violated