postgres key is not present in table constraint

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When trying to ALTER TABLE in Postgres 9.5 to create foreign key constraint: from product_template.product_brand_id to product_brand.id 

ALTER TABLE public.product_template
    ADD CONSTRAINT product_template_product_brand_id_fkey 
    FOREIGN KEY (product_brand_id)
    REFERENCES public.product_brand (id) MATCH SIMPLE
    ON UPDATE NO ACTION
    ON DELETE SET NULL;

Returns error

ERROR:  insert or update on table "product_template" violates foreign key         constraint "product_template_product_brand_id_fkey"
DETAIL:  Key (product_brand_id)=(12) is not present in table "product_brand".
STATEMENT:  ALTER TABLE "product_template" ADD FOREIGN KEY ("product_brand_id") REFERENCES "product_brand" ON DELETE set null

Im confused why postgres is trying to find product_brand.product_brand_id, when the fkey is from product_template.product_brand_id to product_brand.id

Any ideas?

postgresql-9.5 postgresql foreign-keys
2 Answers

In simple terms, the value of FOREIGN KEY(product_brand_id) provided in your ALTER statement is not present in the source (product_brand) table.

user_37109350
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