MySQL questions

[Billy Ng]

I notice the subselect will be in version 4

Billy Ng

"Gerhard Häring" <gerhard at bigfoot.de> wrote in message
news:mailman.1020816014.17321.python-list at python.org...
> * Billy Ng <kwokng at earthlink.net> [2002-05-07 23:33 +0000]:
> > The combination of the user_id and product_id will be uniqe.
>
> You'd make this combination the primary key, then. Just add this to your
> table definition: primary key(user_id, product_id) Fields used for a
> PRIMARY KEY must be NOT NULL.
>
> > When I get the
> > product_id and user_id, i want to change the tableA to see if there is a
> > record that has this user_id and product_id.  If not, I will insert a
record
> > with this user_id and product_id.  What I am doing right is:
> >
> > Query to count tableA whether it has the user_id and product_id
> > if count is 0
> > insert tableA (user_id, product_id) values (xxxxx, xxxxxxx)
> >
> > I think it must a way to write it in one SQL statement.
>
> I don't think this is possible, INSERT and UPDATE are different beasts.
> Sometimes, you can avoid evaluating the SELECT by just DELETEing the
> entry, then INSERTing a new one. If there's no match to the WHERE clause
> in the delete, it won't delete anything, so it's basically the
> non-existant "INSERT OR UPDATE" that you seem to look for.
>
> > > > Question3
> > > > Can I query from a query in MySQL?
> > > >
> > > You mean can the output of one query become the input of another? Only
if
> > > you store the first query's output in a temporary table.
>
> Yes, MySQL doesn't have subselects, which is one of it's many
> weaknesses.
>
> Gerhard
> --
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> reduce(lambda x,y:x+y,map(lambda
x:chr(ord(x)^42),tuple('zS^BED\nX_FOY\x0b')))
>
>
>