Question

i have two tables:

CREATE TABLE "public"."auctions" (
"id" VARCHAR(255) NOT NULL, 
"auction_value_key" VARCHAR(255) NOT NULL, 
"ctime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, 
"mtime" TIMESTAMP WITHOUT TIME ZONE NOT NULL,
 CONSTRAINT "pk_XXXX2" PRIMARY KEY("id"), 
);

and

CREATE TABLE "public"."auction_values" (
 "id" NUMERIC DEFAULT nextval('default_seq'::regclass) NOT NULL, 
 "fk_auction_value_key" VARCHAR(255) NOT NULL, 
 "key" VARCHAR(255) NOT NULL, 
 "value" TEXT, 
 "ctime" TIMESTAMP WITHOUT TIME ZONE NOT NULL, 
 "mtime" TIMESTAMP WITHOUT TIME ZONE NOT NULL,
 CONSTRAINT "pk_XXXX1" PRIMARY KEY("id"), 
);

if i want to create a many-to-many relationship on the auction_value_key like this:

ALTER TABLE "public"."auction_values"
  ADD CONSTRAINT "auction_values_fk" FOREIGN KEY ("fk_auction_value_key")
    REFERENCES "public"."auctions"("auction_value_key")
    ON DELETE NO ACTION
    ON UPDATE NO ACTION
    NOT DEFERRABLE;

i get this SQL error:

ERROR:  there is no unique constraint matching given keys for referenced table "auctions"

Question:

As you might see, i want “auction_values” to be be “reused” by different auctions without duplicating them for every auction… So i don’t want a key relation on the “id” field in the auctions table…

Am i thinking wrong here or what is the deal? 😉

Thanks

Answer 1

You need an extra table to model a many-to-many relationship. It will contain the mappings between auctions and auction_values. It needs two columns: auction_id and auction_value_id.