how to make vertica case insensitive

daniel=> create table vincent (user_name varchar);
CREATE TABLE
daniel=> copy vincent from stdin direct;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> John
>> James
>> Jane
>> Jim
>> jac
>> \.
daniel=> select lower(user_name) from vincent ;
 lower 
-------
 james
 jane
 jim
 john
 jac
(5 rows)

daniel=> select upper(user_name) from vincent ;
 upper 
-------
 JAMES
 JANE
 JIM
 JOHN
 JAC
(5 rows)

daniel=> select * from vincent where user_name ilike 'jac';
 user_name 
-----------
 jac
(1 row)

daniel=> select * from vincent where user_name ilike 'JAC';
 user_name 
-----------
 jac
(1 row)


daniel=> select lower(user_name) from vincent ;
 lower 
-------
 james
 jane
 jim
 john
 jac
(5 rows)

daniel=> select upper(user_name) from vincent ;
 upper 
-------
 JAMES
 JANE
 JIM
 JOHN
 JAC
(5 rows)

daniel=> select * from vincent where user_name ilike 'jac';
 user_name 
-----------
 jac
(1 row)

daniel=> select * from vincent where user_name ilike 'JAC';
 user_name 
-----------
 jac
(1 row)

Thank you all.

@Abhishek,  it works with solution you provided.

Thank you again.
two more questions:

1)Is there any performance impact if changing locale to LEN_S1?

2) where can I find the locale description such as LEN_S1 in the doc?

attach the test for set locale to LEN_S1:

------------------------------------------
vertica=> create table vincent(username varchar(100));
CREATE TABLE
vertica=> insert into vincent values('James');
OUTPUT
--------
1
(1 row)

vertica=> insert into vincent values('james');
OUTPUT
--------
1
(1 row)

vertica=> insert into vincent values('JAMES');
OUTPUT
--------
1
(1 row)

vertica=> commit;
COMMIT
vertica=> select * from vincent;
username
----------
JAMES
James
james
(3 rows)

vertica=> select * from vincent where username like 'JAMES';
username
----------
JAMES
(1 row)

vertica=> select * from vincent where username ilike 'JAMES';
username
----------
JAMES
James
james
(3 rows)

vertica=> set locale to LEN_S1;
INFO 2567: Canonical locale: 'en'
Standard collation: 'LEN_S1'
English
SET
vertica=> select * from vincent where username like 'JAMES';
username
----------
JAMES
James
james
(3 rows)