Question

I can’t understand the usage of the using word. Can you explain me?

SELECT   1
FROM CONF_RAGGR_OPZTAR ropt
    JOIN TAR_OPZIONI_TARIFFARIE OPT using (OPT_OPZIONE_TARIFFARIA_ID)
    JOIN CONF_RAGGRUPPAMENTI_FORN rgf using (RGF_RAGGRUPPAMENTO_FORN_ID)
    JOIN CONF_FORNITURE_REL_RAGG forg using (RGF_RAGGRUPPAMENTO_FORN_ID)
    JOIN CONF_FORNITURE forn using (FORN_FORNITURA_ID)
    LEFT JOIN (
            select *
            from CONF_ELEMENTI_FATTURABILI 
            where ELF_FLAG_ANN = 'N' 
                AND ELF_DATA_VER_FIN = TO_DATE('31/12/9999','DD/MM/YYYY')
        ) elf **using** (ROPT_RAGGR_OPZTAR_ID,COID_CONTRATTUARIO_ID,ROPT_DATA_INI,EDW_PARTITION)
--   LEFT OUTER JOIN TAR_VOCI_FATTURABILI vof
--     ON (elf.VOF_VOCE_FATTURABILE_ID = vof.VOF_VOCE_FATTURABILE_ID)
--   LEFT OUTER JOIN BASE_FASCE_ORARIE fas
--     ON (fas.FAS_FASCIA_ORARIA_ID = elf.FAS_FASCIA_ORARIA_ID)
WHERE FORN_FORNITURA_ID = 'QJlXmOFZPF3eAlAG'
ORDER BY  elf.ELF_VERSIONE DESC; 

Answer 1

The using keyword indicates that this is a natural join. This means that the column names on both side of the join are identical.

In your case this means that you will join both sides on ROPT_RAGGR_OPZTAR_ID, COID_CONTRATTUARIO_ID, ROPT_DATA_INI and EDW_PARTITION.