Fill in bridge table with query - sql

Question

I have four tables, the main purpose of these tables is to have a many to many keyword to message relationship. each keyword can have many messages and each message can have many keywords they are related together if the category id matches.
CREATE TABLE public.trigger_category
(
id integer NOT NULL DEFAULT nextval('trigger_category_id_seq'::regclass),
description text COLLATE pg_catalog."default" NOT NULL,
CONSTRAINT trigger_category_id PRIMARY KEY (id)
)
CREATE TABLE public.trigger_keyword
(
id integer NOT NULL DEFAULT nextval('trigger_keyword_id_seq'::regclass),
keyword text COLLATE pg_catalog."default" NOT NULL,
category_id bigint NOT NULL,
CONSTRAINT trigger_keyword_id PRIMARY KEY (id),
CONSTRAINT trigger_keyword_category_id_fkey FOREIGN KEY (category_id)
REFERENCES public.trigger_category (id) MATCH SIMPLE
ON UPDATE CASCADE
ON DELETE NO ACTION
)
CREATE TABLE public.trigger_message
(
id integer NOT NULL DEFAULT nextval('trigger_message_id_seq'::regclass),
message text COLLATE pg_catalog."default" NOT NULL,
category_id bigint NOT NULL,
CONSTRAINT trigger_message_id PRIMARY KEY (id),
CONSTRAINT trigger_message_category_id_fkey FOREIGN KEY (category_id)
REFERENCES public.trigger_category (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
CREATE TABLE public.trigger_keyword_trigger_message
(
trigger_keyword_id bigint NOT NULL,
trigger_message_id bigint NOT NULL,
CONSTRAINT trigger_keyword_trigger_message_trigger_keyword_id_trigger_mess PRIMARY KEY (trigger_keyword_id, trigger_message_id),
CONSTRAINT trigger_keyword_trigger_message_trigger_keyword_id_fkey FOREIGN KEY (trigger_keyword_id)
REFERENCES public.trigger_keyword (id) MATCH SIMPLE
ON UPDATE CASCADE
ON DELETE NO ACTION,
CONSTRAINT trigger_keyword_trigger_message_trigger_message_id_fkey FOREIGN KEY (trigger_message_id)
REFERENCES public.trigger_message (id) MATCH SIMPLE
ON UPDATE CASCADE
ON DELETE NO ACTION
)
I manually insert keywords in the trigger_keyword table and I manually insert messages in the trigger_message table, if they are related then they would get the same category_id
Is it possible to write a query that would automatically go through the rows and if a keyword and message have the same category_id then it would create all the appropriate rows for the bridge table trigger_keyword_trigger_message?

Answer 1

You could achieve this with an Oracle Merge Query.
The USING clause selects all records to insert, and the WHEN MATCHED does to inserts in the bridge table.
MERGE INTO trigger_keyword_trigger_message tktm
USING (
SELECT tk.id tk_id, tm.id tm_id
FROM
trigger_keyword tk
INNER JOIN trigger_message tm on tm.category_id = tk.category_id
) us
WHEN MATCHED THEN
INSERT (tktm.trigger_keyword_id, tktm.trigger_message_id)
VALUES (us.tk_id, us.tm_id)
;