Re: Foreign key problem

<frebe73_at_gmail.com> wrote in message
news:1150175956.098492.15000_at_i40g2000cwc.googlegroups.com...
> I am working on an application which need a data model that reflects
> the schema structure. My tables are ("*" indicates primary key column):
>
> tableinfo(*table_name)
> columninfo(*table_name, *col_name)
> fk(*fk_name, pk_table, fk_table)
> fk_column(*fk_name, *fk_column, pk_column)
>
> My problem is the last table, fk_column. How can I define a foreign key
> for fk_column.fk_column (and pk_column) referencing the table
> columninfo? The column table_name is not an member of the table
> fk_column, but it could easily be joined from the fk table, but I don't
> think that helps me with defining the foreign key constraint?
>
> The corresponding information_schema tables in MySQL looks like this
> (simplified):
> table_constraints(*constraint_name, table_name)
> key_column_usage(*contraint_name, *table_name, *column_name,
> referenced_table_name, referenced_column_name)
>
> In this case it is possible to define foreign key constraints, but I
> don't consider these tables normalized. The value of table_name is
> given by the constraint_name and should not be repeated in the second
> table.
>
> Somebody that have a pice of advice?
>
> Fredrik Bertilsson
>

At the end of the day, foreign keys is an implementation issue. But Ted Codd had a lot to say about the domain of foreign keys. The "glue".

R Received on Wed Jun 14 2006 - 03:45:42 CEST