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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