Constraints between two or more tables

Dear all,
I have a general question, i searched in Google but i couldn’t find any result.
if i want to add constraints to a table it is easy , but what if in this "Check " part, i also want to consider records from another table? how it is possible?
like this , but it doesn't work actually in oracle 11g :
{code}
ALTER TABLE Country ADD CONSTRAINT "Country_CkHK1"
CHECK (population > ( select sum(ci.population) from city ci where ci.country=code group by code) ) ENABLE;
{code}
thank you in advance.
best,david

Hi,
The only kind of constraint that references 2 tables is a foreign key constraint. All other constraints only refer to 1 table. As Solomon said, you can't do what you want using only constraints.
You can DML create triggers on each table that read the relevant information from the other table, and raise an error if the DML would break your business rules. This would be easiest if you created a view that joined the 2 tables, and created an INSTEAD OF trigger on the view. Do all of the DML through the view, not the actual tables.
For this particular problem (if I understand it correctly), you might consider adding an excess_population column to the country table, that tells how much country.population exceeds the SUM of the related city.populations. This number must always be greater than 0, which you can enforce with a CHECK constraint. The triggers on each table can change excess_population so that it is always up-to-date.

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Dave
"EviePhillips" <[email protected]> wrote in
message
news:[email protected]...
> The CS3 Dreamweaver book says that the WHERE clause can
create a join for
two
> or more tables. The join was created, but the data is
repeating. I have
> searched the web and this forum and have not found the
answer.
>
> My Master page filters the recordset by Style No and
when a customer
clicks on
> a particular style, it sends him to the Detail page. All
the records are
> showing from all tables on the detail page from the
Dynamic List, except
they
> are showing multiple times (ex. Size table has 4 sizes
and Color table has
2
> colors - my Size Drop Down list is showing 8 options and
my Color Drop
Down
> List is showing 8 options) I have a Master Page with a
recordset pointing
to a
> Detail Page using the same recordset.
>
> Master page works perfectly.
> Master Recordset SQL:
> SELECT products.itemID, products.category,
products.styleno,
products.name,
> products.description, products.ourprice,
products.imageTH, products.image,
> coloroption.color, sizeoption.size
> FROM products, coloroption, sizeoption
> WHERE category = 'chefcoats' AND
products.styleno=sizeoption.styleno AND
> products.styleno=coloroption.styleno
> GROUP BY products.styleno
> ORDER BY styleno ASC
>
> The Detail Recordset:
> SELECT products.itemID, products.category,
products.styleno,
products.name,
> products.description, products.ourprice,
products.imageTH, products.image,
> sizeoption.size, coloroption.color
> FROM products, sizeoption, coloroption
> WHERE itemID=colname AND
products.styleno=sizeoption.styleno AND
> products.styleno=coloroption.styleno
>
> I tried using the GROUP BY on the detail page, but then
it only showed
one
> size and color from the dynamic drop down list. I tried
changing the
field
> name "styleno" in the other tables to be unique,
however, I was using the
table
> identifer. I tried using the JOIN command instead of the
WHERE clause and
that
> didn't help either.
>
> On the detail page, the customer is supposed to click on
the Size box and
see
> sizes XSM - 6XL ONLY ONE TIME. and then be able to click
on the Color
option
> and see White, Black, Red ONE TIME.
>
> Is this possible?
>
> Thank you for giving your time to read this.!
> Evie
>
>

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