slow down on UPDATE using IN statements

Hi there,

I was in troubles with a UPDATE+IN statement:

The following command use to take about 5 minutes to
be done:

UPDATE requisicao SET conclusao='3' WHERE reg IN
(SELECT reg FROM requisicao WHERE now()-data>'15
days');

The table 'requisicao' has only about 400 lines (!!).

If I change it to:

UPDATE requisicao SET conclusao='3' WHERE reg IN (12,
45, 87, 98, 129, 350, 389);

I have detected that the major problem isn't in the
amount of lines changed, but in the subselect.

How can I solve/optimize it? I would like to use the
IN, but in the last case I would make a software
change.

Thanks in advance and
Best regards,

Marcelo Pereira
Brazil

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