How to coalesce an empty/null value that is part of Concact string in Postgres?

I have the following CREATE View statement where I am concatenating a couple fields. It grabs the 1st 100 characters of the first field, then appends an integer field

  CREATE OR REPLACE VIEW $"schema_1"."tbl_225_customid" AS 
  SELECT tbl_225.id,
  ("substring"((field_2)::text, 0, 100)::text) ||  ' (' || "field_1" || ')' as fullname
  FROM schema_1.tbl_225;

This works fine when there is data in field_2, however, when field_2 is null, the view shows NULL instead of just the integer part of the expression.

I tried wrapping this in a coalesce statement like this, but it throws an error.

   CREATE OR REPLACE VIEW $"schema_1"."tbl_225_customid" AS 
   SELECT tbl_225.id,
   COALESCE(("substring"((field_2)::text, 0, 100)::text),'') ||  ' (' || "field_1" || ')' as fullname
   FROM schema_1.tbl_225;

How do I write the concat string such that, if field_2 is null, it will use '' for that and still result in value?

Solution

I would recommend simply using string function concat_ws() for this: it ignores null value by design, so you just don't need to worry about them:

select 
    tbl_225.id,
    concat_ws('', substring(field_2::text, 0, 100), ' (' || field_1 || ')') as fullname
from schema_1.tbl_225;