Re: unique amount more than one table

On 04/05/2011 04:02 PM, Perry Smith wrote:
> I have five tables each with a "name" field. Due to limitations in my user interface, I want a name to be unique amoung these five tables.
>
> I thought I could first create a view with something like:
>
> SELECT name, 'table1' as type from table1
> UNION ALL
> SELECT name, 'table2' as type from table2
> UNION ALL
> SELECT name, 'table3' as type from table3
> ...
>
> I called this view xxx (I'm just experimenting right now).
>
> I then created a function:
>
> CREATE OR REPLACE FUNCTION unique_xxx ( ) RETURNS boolean AS $$
> SELECT ( SELECT max(cnt) FROM ( SELECT count(*) AS cnt FROM xxx GROUP BY name ) AS foo ) = 1;
> $$ LANGUAGE SQL;
>
> Next I added a check constraint with:
>
> ALTER TABLE table1 ADD CHECK ( unique_xxx() );
>
> A test shows:
>
> select unique_xxx();
> unique_xxx
> ------------
> t
> (1 row)
>
> After I insert a row that I want to be rejected, I can do:
>
> select unique_xxx();
> unique_xxx
> ------------
> f
> (1 row)
>
> but the insert was not rejected. I'm guessing because the check constraint runs before the insert? So, I could change my approach and have my unique_xxx function see if the name to be added is already in the xxx view but it is at that point that I stopped and thought I would ask for advice. Am I close or am I going down the wrong road?
>
> Thank you for your time,
> pedz
>
>

You might try making a separate name table and having a unique index
there and make the other users of name refer to the new table's name
field. (I would stick on id on the new name table...)