torjehoa_dibblerdummy=> ALTER TABLE products ADD stock integer;

    Table "torjehoa_dibblerdummy.products"
  Column  |         Type          | Modifiers 
----------+-----------------------+-----------
 bar_code | character varying(13) | not null
 name     | character varying(45) | 
 price    | integer               | 
Indexes:
    "products_pkey" PRIMARY KEY, btree (bar_code)

torjehoa_dibblerdummy=> ALTER TABLE products ADD stock integer;
ALTER TABLE
torjehoa_dibblerdummy=> UPDATE products SET stock = 0;
UPDATE 102
torjehoa_dibblerdummy=> ALTER TABLE products ALTER stock SET NOT NULL;
ALTER TABLE
torjehoa_dibblerdummy=> \d products
    Table "torjehoa_dibblerdummy.products"
  Column  |         Type          | Modifiers 
----------+-----------------------+-----------
 bar_code | character varying(13) | not null
 name     | character varying(45) | 
 price    | integer               | 
 stock    | integer               | not null
Indexes:
    "products_pkey" PRIMARY KEY, btree (bar_code)

torjehoa_dibblerdummy=>