CREATE TABLE users (
    id       bigint NOT NULL,
    nome     VARCHAR2(255) NOT NULL,
    email    VARCHAR2(255),
    situacao SMALLINT DEFAULT 1
);

ALTER TABLE users
    ADD CHECK ( situacao IN ( 0, 1 ) );
CREATE UNIQUE INDEX users_email_situacao ON users 
    ( 
      (email )
WHERE
    situacao = 1 
    ) 
;