NULL-input for concatenated string in generated column

Question

I have a table

CREATE TABLE IF NOT EXISTS club.climbers 
(
    climber_id SERIAL PRIMARY KEY,
    climber_first_name VARCHAR(20) NOT NULL,
    climber_last_name VARCHAR(30) NOT NULL,
    climber_full_name TEXT GENERATED ALWAYS AS (climber_first_name || ' ' || climber_last_name) STORED NOT NULL,
    sex_id INTEGER NOT NULL REFERENCES club.sex,
    climber_date_birth DATE NOT NULL,
    climber_phone VARCHAR(20) NOT NULL,
    postal_code_id INTEGER REFERENCES club.postal_codes,
    street VARCHAR(75) NOT NULL,
    building VARCHAR(5) NOT NULL,
    apartment VARCHAR(5),
    full_address TEXT GENERATED ALWAYS AS (street || ',' || building || '-' || apartment) STORED
);

But apartment can be NULL and then full_address would be NULL too. I need to ignore NULL values from apartment.

I tried to use CONCAT and COALESCE, but I don't know how to suppress a dangling '-' when apartment is NULL.

Answer 1

You can include the - in the first argument to coalesce() like:

full_address TEXT GENERATED ALWAYS AS (street || ',' || building || 
    coalesce('-' || apartment, '')) STORED);

Answer 2

One option is to use CASE expression:

full_address TEXT GENERATED ALWAYS AS 
    (street || ',' || case when apartment is not null then building || '-' || apartment 
                           else building end) STORED

which - for inserts as

insert into climbers (street, building, apartment) values ('Wall street', 'A', '10');
insert into climbers (street, building, apartment) values ('5th Avenue', 'B', null);

results in

street          building    apartment   full_address
Wall street     A           10          Wall street,A-10
5th Avenue      B           null        5th Avenue,B

See fiddle.