Re: checking data integrity in a recursive table

Luke Pascoe wrote:
> Hi, I have a table that references itself to create a tree-like structure,
> eg:
>     CREATE TABLE tree (
>         id     SERIAL NOT NULL,
>         name   VARCHAR(255) NOT NULL,
>         parent INT NULL,
>         customer IN NOT NULL,
>         CONSTRAINT parent_key...
>         CONSTRAINT customer_fk FOREIGN KEY (customer) REFERENCES customer
>         );
>     ALTER TABLE tree ADD CONSTRAINT FOREIGN KEY (parent) REFERENCES tree;
> 
> As you can see tree also references the customer table.
> 
> What I need is a CHECK that will ensuer that any given "tree" row has the
> same customer as its parent.
> Remember that "parent" can also be NULL.
> 
> Or would this be better done as a trigger?

Good question.  I don't think you can do actualy SQL lookups in a CHECK.
I think you will need a trigger, either in pl/pgsql or in C using SPI to
issue the lookup queries.

You can have a CHECK clause that deals with multiple columns:
CREATE TABLE friend2 (             firstname CHAR(15),             lastname  CHAR(20),             city      CHAR(15),
          state     CHAR(2)      CHECK (length(trim(state)) = 2),             age       INTEGER      CHECK (age >= 0),
          gender    CHAR(1)      CHECK (gender IN ('M','F')),             last_met  DATE         CHECK (last_met
BETWEEN'1950-01-01'                                           AND CURRENT_DATE),             CHECK
(upper(trim(firstname))!= 'ED' OR                    upper(trim(lastname)) != 'RIVERS'));
 

However, that doesn't help you because you can't reference a column in
another row of the same table.


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