Oracle constraints lowercase - sql

Question

I have to make oracle constraints that checks if username is minimum 3 and maximum 10 lowercase letters.
I have used
constraint usernameSMALLCASE check (
REGEXP_Like(username,'^[a-z]{10}$') or
REGEXP_Like(username,'^[a-z]{9}$') or
REGEXP_Like(username,'^[a-z]{8}$') or
REGEXP_Like(username,'^[a-z]{7}$') or
REGEXP_Like(username,'^[a-z]{6}$') or
REGEXP_Like(username,'^[a-z]{5}$') or
REGEXP_Like(username,'^[a-z]{4}$') or
REGEXP_Like(username,'^[a-z]{3}$')
)
However, it is not working.
Somehow, putting $ is causing problem. But I have to put $ to make sure end of the end of line char is also small case.

Answer 1

Your code should work if your column is declared correctly. But you can drastically simplify it:
constraint usernameSMALLCASE check ( REGEXP_Like(username, '^[a-z]{3,10}$') )
Obviously there are other methods besides regular expressions for handling this. However, you have started down the regular expression route and it is simple enough using one.
If you insist on a fixed length column, you can express this as:
constraint usernameSMALLCASE check ( REGEXP_Like(username, '^[a-z]{3,10} *$') )

Answer 2

Create constraint for
username = lower(username) and length(username) > 3
The max length you can enforce by data type
username VARCHAR2(10 CHAR) NOT NULL
Note, regular expression ^[a-z]{3,10}$ is not fully reliable, see Character Class '[: :]' in Regular Expressions
A non-working example is this one:
ALTER SESSION SET NLS_SORT = XSPANISH;
BEGIN
IF REGEXP_LIKE('ch', '^[a-d]$') THEN
DBMS_OUTPUT.PUT_LINE('TRUE');
ELSE
DBMS_OUTPUT.PUT_LINE('FALSE');
END _IF;
END;
Returns TRUE (despite h is not between a-d) because ch in traditional Spanish is considered as one sorting character.
I think a 100% reliable constraint would be like this:
REGEXP_LIKE(TRANSLATE(username, 'abcdefghijklmnopqrstuvwxyz', '**************************'), '^\*{3,10}$')
AND username NOT LIKE '%*%'