Why does the zipcode fail the check constraint? - sql

Question

I feel like I am probably missing something really simple, but I really can't figure out what I'm doing wrong. I'm trying to use a check constraint to make sure zipcodes are 5 digit numbers, but the check restraint keeps failing. Here is the table creating with the constraint:
Create Table Students (
StudentID Int Primary Key Identity(1,1)
StudentNumber nVarchar(100) Unique Not Null,
...
StudentZipCode nChar(10) Not Null
)
Go
Alter Table Students Add Constraint chZipCode
CHECK (StudentZipCode LIKE '[0-9][0-9][0-9][0-9][0-9]' OR StudentZipCode
Like '[0-9][0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]')
Go
Codes like 12345-6789 work, but when I try to insert the values like '12345' or '01234' it gives me this error:
The INSERT statement conflicted with the CHECK constraint "chZipCode". The conflict occurred in database ..., table "dbo.Students", column 'StudentZipCode'.

Answer 1

It fails because you defined the zip code as a char() instead of a varchar(). Hence, it has a bunch of spaces padding it out.
So, define it as:
Create Table Students (
StudentID Int Primary Key Identity(1,1),
StudentNumber nVarchar(100) Unique Not Null,
StudentZipCode nVarChar(10) Not Null,
CHECK (StudentZipCode LIKE '[0-9][0-9][0-9][0-9][0-9]' OR
StudentZipCode LIKE '[0-9][0-9][0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]')
);
Then '12345' works, because it matches the first of the LIKE patterns.
'012344' does not work, because no pattern has six digits in a row.
Here is a SQL Fiddle.