ERROR: could not create exclusion constraint - postgresql

Question

I have a table:
CREATE TABLE attendances
(
id_attendance serial PRIMARY KEY,
id_user integer NOT NULL
REFERENCES users (user_id) ON UPDATE CASCADE ON DELETE CASCADE,
entry_date timestamp with time zone DEFAULT NULL,
departure_date timestamp with time zone DEFAULT NULL,
created_at timestamp with time zone DEFAULT current_timestamp
);
I want to add an exclusion constraint avoiding attendance to overlap (There can be multiple rows for the same day, but time ranges cannot overlap).
So I wrote this code to add the constraint:
ALTER TABLE attendances
ADD CONSTRAINT check_attendance_overlaps
EXCLUDE USING GIST (box(
point(
extract(epoch from entry_date at time zone 'UTC'),
id_user
),
point(
extract(epoch from departure_date at time zone 'UTC') - 0.5,
id_user + 0.5
)
)
WITH && );
But when I tried to run it on the database I got this error:
Error: could not create exclusion constraint "check_attendance_overlaps"

Answer 1

To exclude overlapping time ranges per user, work with a multicolumn constraint on id_user and a timestamptz range (tstzrange).
You need the additional module btree_gist once per database:
CREATE EXTENSION IF NOT EXISTS btree_gist;
Then:
ALTER TABLE attendances ADD CONSTRAINT check_attendance_overlaps
EXCLUDE USING gist (id_user WITH =
, tstzrange(entry_date, departure_date) WITH &&)
See:
Store the day of the week and time?
Postgres constraint for unique datetime range
Or maybe spgist instead of gist. Might be faster. See:
Perform this hours of operation query in PostgreSQL
Of course, there cannot be overlapping rows in the table, or adding the constraint will fail with a similar error message.