PostgreSQL CHECK Constraint on columns other than foreign keys - sql

Question

I have a situation where I want to create a table that associates records from other tables by the id. A constraint of the association is that the year must be the same in the record being associated in each table... Is there a way to get PostgreSQL to CHECK this condition on INSERT?
Table 1:
CREATE TABLE "tenant"."report" (
"id" UUID NOT NULL DEFAULT "pascal".uuid_generate_v1(),
CONSTRAINT "report_pkc_id" PRIMARY KEY ("id"),
"reporting_period" integer NOT NULL,
"name" VARCHAR(64) NOT NULL,
CONSTRAINT "report_uc__name" UNIQUE ("reporting_period", "name"),
"description" VARCHAR(2048) NOT NULL
);
Table 2:
CREATE TABLE "tenant"."upload_file" (
"id" UUID NOT NULL DEFAULT "pascal".uuid_generate_v1(),
CONSTRAINT "upload_file_pkc_id" PRIMARY KEY ("id"),
"file_name" VARCHAR(256) NOT NULL,
"reporting_period" integer
)
Association Table:
CREATE TABLE "tenant"."report_upload_files"
(
"report_id" UUID NOT NULL,
CONSTRAINT "report_upload_files_pkc_tenant_id" PRIMARY KEY ("report_id"),
CONSTRAINT "report_upload_files_fkc_tenant_id" FOREIGN KEY ("report_id")
REFERENCES "tenant"."report" ("id") MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE,
"upload_file_id" UUID NOT NULL,
CONSTRAINT "report_upload_files_fkc_layout_id" FOREIGN KEY ("upload_file_id")
REFERENCES "tenant"."upload_file" ("id") MATCH SIMPLE
ON UPDATE CASCADE ON DELETE CASCADE
)
I want to add something like to the association table CREATE statement:
CHECK ("tenant"."report"."reporting_period" = "tenant"."upload_file"."reporting_period")

Answer 1

You're solving problems that you've created yourself.
Your data model is a typical one-to-many relationship. You don't need an association table. Also, you don't need the same column in two related tables, one of them is redundant. Use the model as shown below to avoid typical problems resulting from lack of normalization.
create table tenant.report (
id uuid primary key default pascal.uuid_generate_v1(),
reporting_period integer not null,
name varchar(64) not null,
description varchar(2048) not null,
unique (reporting_period, name)
);
create table tenant.upload_file (
id uuid primary key default pascal.uuid_generate_v1(),
report_id uuid references tenant.report(id),
file_name varchar(256) not null
);
Using this approach there's no need to ensure that the reporting periods match between the associated records.
BTW, I would use text instead of varchar(n) and integer (serial) instead of uuid.

Answer 2

Using a TRIGGER function I was able to achieve the desired effect:
CREATE FUNCTION "tenant".report_upload_files_create() RETURNS TRIGGER AS
$report_upload_files_create$
BEGIN
IF NOT EXISTS (
SELECT
*
FROM
"tenant"."report",
"tenant"."upload_file"
WHERE
"tenant"."report"."id" = NEW."report_id"
AND
"tenant"."upload_file"."id" = NEW."upload_file_id"
AND
"tenant"."report"."reporting_period" = "tenant"."upload_file"."reporting_period"
)
THEN
RAISE EXCEPTION 'Report and Upload File reporting periods do not match';
END IF;
RETURN NEW;
END
$report_upload_files_create$ LANGUAGE plpgsql;
CREATE TRIGGER "report_upload_files_create" BEFORE INSERT ON "tenant"."report_upload_files"
FOR EACH ROW EXECUTE PROCEDURE "tenant".report_upload_files_create();