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Hello,
On 08/29/2014 03:16 PM, Adrian Klaver wrote:
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)
This is exactly what I plan to do.
So, according to the test result, can make conclusion
that pg_attribute will auto take care of all dependent views.
>> Here is what I did. I would definitely test first and run
in a transaction:
It seems that there is no transaction block needed? The one line
command is:
UPDATE pg_attribute SET atttypmod = -1 WHERE attrelid =
'table_name'::regclass AND attname = 'col1';
Isn't it?
As for the "definitely test", you mean check view after the change?
Would there be any other potential problems for this approach?
If not, I will adopt this approach since we have many view
dependencies and it seems that this was the best way to avoid view
drop/re-creation for now. If there are other ways, please do let me
know.
Thanks a lot!
Emi
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