Are these database schemes correct? - postgresql

Question

I am making a polling system where each poll has multiple choices and a user can make multiple choices. And I would like to know if these schemes were correct
Namely:
A guild cannot have two polls with the same id (Composite key)
A poll cannot have multiple choices with the same id (Composite key)
A user cannot make the same choice several times on a poll (Composite key)
CREATE TABLE IF NOT EXISTS guilds_polls
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
PRIMARY KEY (guild_id, poll_id),
FOREIGN KEY (guild_id) REFERENCES guilds (id) ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS guilds_polls_choices
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
choice_id INT NOT NULL,
choice VARCHAR(255) NOT NULL,
PRIMARY KEY (guild_id, poll_id, choice_id),
FOREIGN KEY (guild_id, poll_id) REFERENCES guilds_polls (guild_id, poll_id) ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS guilds_polls_user_choices
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
choice_id BIGINT NOT NULL,
user_id BIGINT NOT NULL,
PRIMARY KEY (guild_id, poll_id, user_id, choice_id),
FOREIGN KEY (guild_id, poll_id) REFERENCES guilds_polls (guild_id, poll_id) ON DELETE CASCADE
);

Answer 1

LGTM.
But there is a small improvement we could make. Polls and choices is actually a n:n relation. That means multiple polls can have the same choice (A lot of polls are probably going to have the choices "no" and "yes") and one poll can have multiple choices (obviously). In your schema, you modeled it as a 1:n relation (every poll has multiple choices, but every choice has only one poll).
The solution would be to create a separate table Choices and then introduce a connecting table, which glues the choices to the polls. This way you have one table more, but a lot less duplicate data:
CREATE TABLE IF NOT EXISTS guilds_polls
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
PRIMARY KEY (guild_id, poll_id),
FOREIGN KEY (guild_id) REFERENCES guilds (id) ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS guilds_polls_choices
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
choice_id INT NOT NULL,
PRIMARY KEY (guild_id, poll_id, choice_id),
FOREIGN KEY (guild_id, poll_id) REFERENCES guilds_polls (guild_id, poll_id) ON DELETE CASCADE,
FOREIGN KEY (choice_id) REFERENCES choices (choice_id) ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS choices
(
choice_id INT NOT NULL,
choice VARCHAR(255) NOT NULL,
PRIMARY KEY (choice_id),
);
CREATE TABLE IF NOT EXISTS guilds_polls_user_choices
(
guild_id BIGINT NOT NULL,
poll_id varchar(8) NOT NULL,
choice_id BIGINT NOT NULL,
user_id BIGINT NOT NULL,
PRIMARY KEY (guild_id, poll_id, user_id, choice_id),
FOREIGN KEY (guild_id, poll_id) REFERENCES guilds_polls (guild_id, poll_id) ON DELETE CASCADE,
-- you also forgot this foreign key:
FOREIGN KEY (choice_id) REFERENCES choices (choice_id) ON DELETE CASCADE
);
Disclaimer: not a PostgreSQL expert, so the syntax could be off.
Database modeling relies heavily on normalization (https://en.wikipedia.org/wiki/Database_normalization). Every database should follow the first 3 Normal Forms.