DUAL
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Spiegazione
E' possibile specificare DUAL come tabella fittizia, nelle situazioni in cui nessuna tabella è coinvola:
MariaDB [(none)]> SELECT 1 + 1 FROM DUAL; +-------+ | 1 + 1 | +-------+ | 2 | +-------+
DUAL is purely for the convenience of people who require
that all SELECT statements should have
FROM and possibly other clauses. MySQL may ignore the
clauses. MariaDB does not require FROM DUAL if no tables
are referenced.
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