Changing the type of a column used in other views

问题

create table base (name character varying(255));                                                                                                                                                        
create view v1 as select *, now() from base;                                                        
create view v2 as select * from v1 where name = 'joe';
alter table base alter column name type text;

Gives this error:

cannot alter type of a column used by a view or rule
DETAIL:  rule _RETURN on view v1 depends on column "name"

This is sort of annoying, because now I have to recreate all the views that reference the base.name column. It's especially annoying when I have views that reference other views.

What I'd love to be able to do is something like:

select recreate_views('v1', 'v2', 'alter table base alter column name type text');

And have the function get the view definitions for v1 and v2, drop them, run the code specified, then recreate v1 and v2. If I could use Ruby, I'd probably have the function take a function/block/lambda, like

recreate_views 'v1', 'v2' do
  alter table base alter column name type text
end

Is something like this possible? Are there utilities out there that do something similar?

回答1:

I think this does what you want, though I moved the view list to the end of args to be compatible with VARIADIC semantics.

CREATE OR REPLACE FUNCTION recreate_views(run_me text, VARIADIC views text[])
  RETURNS void
AS  $$
DECLARE
  view_defs text[];
  i integer;
  def text;
BEGIN
  for i in array_lower(views,1) .. array_upper(views,1) loop
    select definition into def from pg_views where viewname = views[i];
    view_defs[i] := def;
    EXECUTE 'DROP VIEW ' || views[i];
  end loop;

  EXECUTE run_me;

  for i in reverse array_upper(views,1) .. array_lower(views,1) loop
    def = 'CREATE OR REPLACE VIEW ' || quote_ident( views[i] ) || ' AS ' || view_defs[i];
    EXECUTE def;
  end loop;

END
$$
LANGUAGE plpgsql;

回答2:

an improvment would be to check before trying to drop view if it exists at all, otherwise you will get an error, so do like this :

for i in array_lower(views,1) .. array_upper(views,1) loop
    select definition into def from pg_views where viewname = views[i];
    view_defs[i] := def;
    IF def IS NOT NULL THEN
        EXECUTE 'DROP VIEW ' || schema_name || '.' || views[i];
    END IF;
end loop;   

    EXECUTE run_me;

for i in reverse array_upper(views,1) .. array_lower(views,1) loop
    IF view_defs[i] IS NOT NULL THEN
        def = 'CREATE OR REPLACE VIEW ' || schema_name || '.' || views[i] || ' AS ' || view_defs[i];
        EXECUTE def;
    END IF;
end loop;

来源：https://stackoverflow.com/questions/9711405/changing-the-type-of-a-column-used-in-other-views

标签

postgresql

views