Operation eq with varchar

HI ALL,

I don't no why i can't compare varchar with string const :

CREATE TABLE XXX (
     id   integer,
     stvarchar varchar
) ;


SELECT * FROM XXX WHERE stvarchar = 'somestring' ;

I can only use like operator :

SELECT * FROM XXX WHERE stvarchar like 'somestring%' ;

Any body know why ?

I have the 7.1.3 verion in redhat 7.2


Best Regards,
Ngoc-Khoi TO.