Counting Rows

[Steven]

Hi there,

I have an admin system (Add/Modify/Delete) for two types of records in the
database. They have a Parent - Child relationship

My problem is that I want to display on the "parent" record whether the
child exists or not .

The records are found in two different tables, but have the same Primary
Key.

Any ideas

cheers

Steven

[Chris Hope]

Re: Counting Rows

Steven wrote:
[color=blue]
> I have an admin system (Add/Modify/Delete) for two types of records in the
> database. They have a Parent - Child relationship
>
> My problem is that I want to display on the "parent" record whether the
> child exists or not .
>
> The records are found in two different tables, but have the same Primary
> Key.[/color]

You'll be wanting to use a LEFT JOIN then. With a left join you can show all
the results from the first table whether or not there is a related record
from the second/joined table. The columns that would have been displayed
from the second table will all be NULL.

--
Chris Hope - The Electric Toolbox - http://www.electrictoolbox.com/

[Paul Robson]

Re: Counting Rows

Steven wrote:
[color=blue]
> Hi there,
>
> I have an admin system (Add/Modify/Delete) for two types of records in the
> database. They have a Parent - Child relationship
>
> My problem is that I want to display on the "parent" record whether the
> child exists or not .
>[/color]

Left Join. If you select [stuff] from table 1 left join table 2 on [stuff]
then every record in table 1 will appear ; if there aren't child record(s)
in table 2 for table 1 then the corresponding field will be null.
[color=blue]
> The records are found in two different tables, but have the same Primary
> Key.[/color]

I don't think you mean this :) they'll have different primary keys but a
foreign key in the child .

[Tony Marston]

Re: Counting Rows


"Paul Robson" <autismuk@autis muk.muralichuck s.freeserve.co. uk> wrote in
message news:cktatu$3qb $2@newsg3.svr.p ol.co.uk...[color=blue]
> Steven wrote:
>[color=green]
>> Hi there,
>>
>> I have an admin system (Add/Modify/Delete) for two types of records in
>> the
>> database. They have a Parent - Child relationship
>>
>> My problem is that I want to display on the "parent" record whether the
>> child exists or not .
>>[/color]
>
> Left Join. If you select [stuff] from table 1 left join table 2 on [stuff]
> then every record in table 1 will appear ; if there aren't child record(s)
> in table 2 for table 1 then the corresponding field will be null.
>[color=green]
>> The records are found in two different tables, but have the same Primary
>> Key.[/color]
>
> I don't think you mean this :) they'll have different primary keys but a
> foreign key in the child .
>[/color]

It is possible for the primary key on the child table to be exactly the same
as the foreign key which links to the parent table. This is the way to
enforce a one-to-one relationship. If the child table has a different
primary key it will allow a one-to-many relationship which may not be
desirable.

--
Tony Marston

http://www.tonymarston.net