title: How to create foreign key in Cassandra CQL
body: <p>I'm trying to replicate a SQL database in Cassandra, but, while I had no problem creating the tables, I found that I cannot find an example easy to understand that shows how I can create foreign keys in Cassandra.</p>
  
  <p>So, If I have this in SQL:</p>
  
  <pre><code>CREATE TABLE COOP_USUARIO (
   CI                   VARCHAR2 (13 BYTE) NOT NULL ,
   CUENTA               VARCHAR2 (20 BYTE) NOT NULL ,
   NOMBRE               VARCHAR2 (50 BYTE) NOT NULL ,
   EMAIL                VARCHAR2 (255 BYTE) NOT NULL ,
   DIRECCION            VARCHAR2 (255 BYTE) ,
   CIUDAD               NUMBER NOT NULL ,
   TELEFONO             VARCHAR2 (10 BYTE) NOT NULL ,
   TIPO_PERSONA         NUMBER (1) NOT NULL ,
  );
   CREATE UNIQUE INDEX COOP_USUARIO_PK ON COOP_USUARIO(
   CI ASC
  );
  ALTER TABLE COOP_USUARIO ADD CONSTRAINT COOP_USUARIO_PK PRIMARY KEY ( CI ) ;
  
  CREATE TABLE COOP_CIUDADES
  (
   ID        NUMBER NOT NULL ,
   NOMBRE    VARCHAR2 (25 BYTE) NOT NULL ,
   PROVINCIA NUMBER NOT NULL
  ) ;
  CREATE UNIQUE INDEX COOP_CIUDADES_PK ON COOP_CIUDADES
  (
    ID ASC
  );
  ALTER TABLE COOP_CIUDADES ADD CONSTRAINT COOP_CIUDADES_PK PRIMARY KEY ( ID ) ;
  
  
  ALTER TABLE COOP_USUARIO ADD CONSTRAINT COOP_USUARIO_CIUDADES_FK FOREIGN KEY ( CIUDAD ) REFERENCES COOP_CIUDADES ( ID ) ;
  </code></pre>
  
  <p>What is the Cassndra CQL code for the same purpose?</p>