Set default value in PostrgreSQL table column to a value from a query

You can't do that on DEFAULT. However you could use a trigger before insert checking if there is a NULL value.

You can check the PostgreSQL Trigger Documentation here

1. Create a function to get the id from the table users with email as an arg.

   CREATE OR REPLACE FUNCTION id_in_users(iemail varchar) RETURNS int LANGUAGE SQL AS
   $$ SELECT id FROM users WHERE email = iemail; $$;
   

2. And alter the table

   ALTER TABLE runs ADD COLUMN userId bigint NOT NULL DEFAULT     
   id_in_users('[email protected]');
   

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