Re: View not allowing to drop column (Bug or Feature enhancement )

Hello

On 05/16/2016 08:49 AM, Shrikant Bhende wrote:
> Hi all,
>
> While working on the view I came across an unusual behaviour of the view,
> PostgreSQL do not allows to drop a column from the view, whereas same
> pattern of Create and Replace view works while adding a column.
>
> Please find below test for the same.
>
> *
> *
> *Version info *
> *===========*
> postgres=# select version();
>                                                   version
> ----------------------------------------------------------------------------------------------------------
>   PostgreSQL 9.5.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.1.2
> 20080704 (Red Hat 4.1.2-55), 64-bit
> (1 row)
> \d+ orgdata
>                  Table "public.orgdata"
>   Column  |         Type          | Modifiers | Storage  | Stats target
> | Description
> ---------+-----------------------+-----------+----------+--------------+-------------
>   id      | integer        | not null  | plain    |              |
>   name    | character varying(20) | not null  | extended |              |
>   address | character varying(20) |           | extended |              |
>   age     | integer        | not null  | plain    |              |
>   salary  | numeric(10,0)        |           | main     |              |
> Indexes:
>      "orgdata_pkey" PRIMARY KEY, btree (id)
> Triggers:
>      example_trigger AFTER INSERT ON orgdata FOR EACH ROW EXECUTE
> PROCEDURE auditlogfunc()
>
> *Creating view *
> postgres=# create or replace view vi1  as
> select id , name from orgdata ;
> CREATE VIEW
>
> *Alter command do not have any option to drop column*
> postgres=# alter view vi1
> ALTER COLUMN  OWNER TO      RENAME TO     SET SCHEMA

Neither there is an option to add a column.

> *
> *
> *To add columns it will work.*
> *========================*
> postgres=# create or replace view vi1 as
> postgres-# select id, name, age from orgdata ;
> CREATE VIEW

What you are doing is actually a CREATE OR REPLACE VIEW and not a ALTER
VIEW. In this case it is allowed to add columns *at the end of the list*
(see below).

> *
> *
> *While trying to drop a column by replacing view definition from view it
> throws an error saying cannot drop column from view.*
> *=====================================================================*
> postgres=# create or replace view vi1 as select
> id , name from orgdata ;
> *ERROR:  cannot drop columns from view*

You need to drop the view before recreating it. Then it works. If you
changed the access to the view with grants or revokes, you also neet to
recreate them. They are dropped with the view.

> If its not a bug and a limitation kindly guide me towards any
> documentation where it is mentioned.

http://www.postgresql.org/docs/current/static/sql-createview.html

CREATE OR REPLACE VIEW is similar, but if a view of the same name
already exists, it is replaced. The new query must generate the same
columns that were generated by the existing view query (that is, the
same column names in the same order and with the same data types), but
it may add additional columns to the end of the list. The calculations
giving rise to the output columns may be completely different.

Regards,
Charles

>
> Thanks.
> --
> Shrikant Bhende
> +91-9975543712

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