I will answer my own question
It is supported out of the box   in 
org.keycloak.models.jpa.entities UserEntity 

    
    
@Table(name="USER_ENTITY", uniqueConstraints = {
        @UniqueConstraint(columnNames = { "REALM_ID", "USERNAME" }),
        @UniqueConstraint(columnNames = { "REALM_ID", "EMAIL_CONSTRAINT" })

    Cool stuff,

    George 

    

    

    

    

    

    

    

    
On 06/12/2015 01:07 PM, George Leon
      wrote:

    

    

      

      

      Hi Keycloak Team ,
      

      

      

      

      Best way to add Unique constraint  to username and email in
      Keycloak ?
      

      

      

      Best Regards
      

      George Leon