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...)
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