Re: alter column to varchar without view drop/re-creation

On 08/29/2014 12:09 PM, Emi Lu wrote:
>
>> Hello list,
>>
>> May I know is there a way to "alter column type to varchar" (previous
>> is varchar(***)) without view drop/re-creation?
>>
>> Basically, looking for a way to change column without have to
>> drop/re-create dependent views.
>>
>> varchar(***) to varchar and no date/numeric changes.
>>
> I saw docs mention about: update pg_attribute. May I know:
>
> . will dependent views updated automatically or there might be potential
> problems?
> . If it's fine, will the following SQL enough to change column from
> varchar(***) to varchar?
>
> update pg_attribute set atttypmod =-1
> where attrelid = 'oid' ;

Here is what I did. I would definitely test first and run in a transaction:

test=# SELECT version();
version

--------------------------------------------------------------------------------------------------------------------------
PostgreSQL 8.3.23 on i686-pc-linux-gnu, compiled by GCC gcc (SUSE
Linux) 4.7.2 20130108 [gcc-4_7-branch revision 195012]

test=# create TABLE base_tbl (id integer, vc_fld varchar(10));
CREATE TABLE
test=# CREATE view v_test as SELECT * from base_tbl ;
CREATE VIEW
test=# insert INTO base_tbl VALUES(1, 'one');
INSERT 0 1
test=# insert INTO base_tbl VALUES(2, 'two');
INSERT 0 1
test=# \d base_tbl
Table "public.base_tbl"
Column | Type | Modifiers
--------+-----------------------+-----------
id | integer |
vc_fld | character varying(10) |

test=# \d v_test
View "public.v_test"
Column | Type | Modifiers
--------+-----------------------+-----------
id | integer |
vc_fld | character varying(10) |
View definition:
SELECT base_tbl.id, base_tbl.vc_fld
FROM base_tbl;

test=# UPDATE pg_attribute SET atttypmod = -1 WHERE attrelid =
'base_tbl'::regclass AND attname = 'vc_fld';
UPDATE 1
test=# UPDATE pg_attribute SET atttypmod = -1 WHERE attrelid =
'v_test'::regclass AND attname = 'vc_fld';
UPDATE 1
test=# \d base_tbl
Table "public.base_tbl"
Column | Type | Modifiers
--------+-------------------+-----------
id | integer |
vc_fld | character varying |

test=# \d v_test
View "public.v_test"
Column | Type | Modifiers
--------+-------------------+-----------
id | integer |
vc_fld | character varying |
View definition:
SELECT base_tbl.id, base_tbl.vc_fld
FROM base_tbl;

test=# insert INTO base_tbl VALUES(3, '123456789012345678901234567890');
INSERT 0 1
test=# SELECT * from base_tbl ;
id | vc_fld
----+--------------------------------
1 | one
2 | two
3 | 123456789012345678901234567890
(3 rows)

test=# SELECT * from v_test ;
id | vc_fld
----+--------------------------------
1 | one
2 | two
3 | 123456789012345678901234567890
(3 rows)

>
> Thanks a lot!
>
>> ---
>> *PostgreSQL 8.3.18 on x86_64*
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com