Postgresql generated column fails when concating not null columns

Question

I have this table definition in pgAdmin4:

CREATE TABLE IF NOT EXISTS cdr_event
(
    id bigint primary key generated always as identity,
    start_time timestamptz NOT NULL DEFAULT now(),
    end_time timestamptz NULL,
    group_id VARCHAR(10) NOT NULL,
    environment VARCHAR(10) NOT NULL,     
    level VARCHAR(10) NOT NULL,           
    schema VARCHAR(30) NOT NULL,      
    instance INTEGER NOT NULL,            
    hive_instance_db_name VARCHAR(100) GENERATED ALWAYS AS (group_id||'_'||environment||'_'||level||'_'||schema||'_'||instance) STORED,
    hive_static_db_name VARCHAR(100) GENERATED ALWAYS AS (group_id||'_'||environment||'_'||level||'_'||schema) STORED,
);

this fails with

ERROR:  generation expression is not immutable
SQL state: 42P17

Why does postgres consider the concat mutable when the dependent columns are all NOT NULL? This thread suggests it should work

Is there anyway to create a concat-ed generated column without creating a custom concat function?

Thanks

Jim Jones Jim Jones · Accepted Answer · 2021-08-11T11:09:24

Try keeping the involved columns of the same type, e.g. casting instance to text should do the trick:

CREATE TABLE IF NOT EXISTS cdr_event
(
    id bigint primary key generated always as identity,
    start_time timestamptz NOT NULL DEFAULT now(),
    end_time timestamptz NULL,
    group_id VARCHAR(10) NOT NULL,
    environment VARCHAR(10) NOT NULL,     
    level VARCHAR(10) NOT NULL,           
    schema VARCHAR(30) NOT NULL,      
    instance INTEGER NOT NULL,            
    hive_instance_db_name VARCHAR(100) GENERATED ALWAYS AS (group_id||'_'||environment||'_'||level||'_'||schema||'_'||instance::text) STORED,
    hive_static_db_name VARCHAR(100) GENERATED ALWAYS AS (group_id||'_'||environment||'_'||level||'_'||schema) STORED
);

Consider using text instead of varchar.

Demo: db<>fiddle

Postgresql generated column fails when concating not null columns

1 Answers