prova così:
oppure:codice:SELECT t1.id_Clienti, t1.data_ordine FROM ordini AS t1 INNER JOIN ordini AS t2 ON t1.id_Clienti = t2.id_Clienti WHERE t2.data_ordine IS NULL
[code]
codice:SELECT t1.id_Clienti, t1.data_ordine FROM ordini AS t1 INNER JOIN ordini AS t2 ON t1.id_Clienti = t2.id_Clienti WHERE t2.data_ordine = ''
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