Re: Add Foreign Keys To Table

You have a wrong concept of foreign keys. "sta_type" is not a key of table
station_type, which cannot be referened as a foreign key.

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From: "Rich Shepard" <rshepard(at)appl-ecosys(dot)com>
Sent: Friday, July 08, 2011 1:40 AM
To: <pgsql-general(at)postgresql(dot)org>
Subject: [GENERAL] Add Foreign Keys To Table

> I'm having difficulty finding the correct syntax to modify an existing
> table. The modification is to add two columns, each a foreign reference to
> the two key columns of another table.
>
> The other table:
>
> CREATE TABLE station_type (
> sta_type VARCHAR(50),
> secondary_type VARCHAR(50),
> natural_indic BOOL,
> PRIMARY KEY (sta_type, secondary_type)
> );
>
> When I try to alter the other table to add columns:
> sta_type VARCHAR(50) REFERENCES station_type(sta_type) and
> secondary_type VARCHAR(50) REFERENCES station_type(secondary_type)
> I get syntax errors. For example,
>
> alter table station_information add column sta_type varchar(50) references
> station_type(sta_type);
> ERROR: there is no unique constraint matching given keys for referenced
> table "station_type"
>
> alter table station_information add column sta_type varchar(50) not null
> references station_type(sta_type);
> ERROR: there is no unique constraint matching given keys for referenced
> table "station_type"
>
> alter table station_information add column sta_type varchar(50)
> unique not null references station_type(sta_type);
> NOTICE: ALTER TABLE / ADD UNIQUE will create implicit index
> "station_information_sta_type_key" for table "station_information"
> ERROR: there is no unique constraint matching given keys for referenced
> table "station_type"
>
> Reading the alter table document page for 9.x does not show me what I'm
> doing incorrectly.
>
> Rich
>
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