Problem with Postgres ALTER TABLE

Question

I have one problem with the ALTER TABLE in postgre. I want to change size of the varchar column. When I try to do this, It says that the view is dependent on that column. I can\

Answer 1

I ran into this problem today and found a work around to avoid dropping and recreating the VIEW . I cannot just drop my VIEW because it is a master VIEW that has many dependent VIEWs built on top of it. Short of having a rebuild script to DROP CASCADE and then recreate ALL of my VIEWs this is a work around.

I change my master VIEW to use a dummy value for the offending column, altered the column in the table, and switched my VIEW back to the column. Using a setup like this:

CREATE TABLE base_table
(
  base_table_id integer,
  base_table_field1 numeric(10,4)
);

CREATE OR REPLACE VIEW master_view AS 
  SELECT
    base_table_id AS id,
    (base_table_field1 * .01)::numeric AS field1
  FROM base_table;

CREATE OR REPLACE VIEW dependent_view AS 
  SELECT
    id AS dependent_id,
    field1 AS dependent_field1
  FROM master_view;

Trying to alter base_table_field1 type like this:

ALTER TABLE base_table ALTER COLUMN base_table_field1 TYPE numeric(10,6);

Will give you this error:

ERROR:  cannot alter type of a column used by a view or rule
DETAIL:  rule _RETURN on view master_view depends on column "base_table_field1"

If you change master_view to use a dummy value for the column like this:

CREATE OR REPLACE VIEW master_view AS 
  SELECT
    base_table_id AS id,
    0.9999 AS field1
  FROM base_table;

Then run your alter:

ALTER TABLE base_table ALTER COLUMN base_table_field1 TYPE numeric(10,6);

And switch your view back:

CREATE OR REPLACE VIEW master_view AS 
  SELECT
    base_table_id AS id,
    (base_table_field1 * .01)::numeric AS field1
  FROM base_table;

It all depends on if your master_view has an explicit type that does not change. Since my VIEW uses '(base_table_field1 * .01)::numeric AS field1' it works, but 'base_table_field1 AS field1' would not because the column type changes. This approach might help in some cases like mine.