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Posted by Captain Paralytic on 10/25/06 10:05
Rik wrote:
> Chung Leong wrote:
> > Daz wrote:
> >> The problem is that when I have a few hundred results to compare.
> >> Should I really query the database that many times? Could I do it
> >> with a single query, and if so, how would I know what items the user
> >> already owns a particular item, and update the database using the
> >> PHP-MySQL layer. To my understanding, you can't execute and UPDATE
> >> or INSERT statement from within a SELECT statement. Nor can you
> >> execute several statements, such as multiple UPDATE statements or
> >> several INSERT statements all in 1.
> >
> > No, that still wouldn't remove the race condition. What you want to do
> > is put a unique constraint on the table, then have your script just
> > perform the INSERT. If it fails, then you know you have a duplicate.
> > MySQL also support the INSERT ... ON DUPLICATE KEY UPDATE syntax I
> > believe.
>
> Yup, or the shorter REPLACE INTO which does exactly the same.
REPLACE INTO does not do exactly the same as INSERT ... ON DUPLICATE
KEY UPDATE
REPLACE INTO deletes a row that is already there and replaces it with a
new row containing values only for fields you supply.
INSERT ... ON DUPLICATE KEY UPDATE simply changes any values you ask it
to on an existing row, leaving any fields that you haven't mentioned
intact.
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