postgresql 数据库 alter table alter column set default 的一些实践
os: centos 7.4
db: postgresql 10.11
创建表后，有时需要对表进行 set default 或者 drop default 设置。
版本
# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core)
#
# su - postgres
$
$ psql -c "select version();"
version
----------------------------------------------------------------------------------------------------------
PostgreSQL 10.11 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)
create table
$ psql
psql (10.11)
Type "help" for help.
postgres=# \timing on
Timing is on.
postgres=#
postgres=# drop table if exists tmp_t4;
DROP TABLE
Time: 313.287 ms
postgres=# create table tmp_t4(
id int8,
name varchar(100),
memo1 varchar(100),
memo2 varchar(100)
);
CREATE TABLE
Time: 360.530 ms
postgres=# insert into tmp_t4
select id,
md5(id::varchar),
md5(id::varchar),
null
from generate_series(1,10000000) as id;
INSERT 0 10000000
Time: 58346.187 ms (00:58.346)
postgres=# select * from tmp_t4 limit 5;
id | name | memo1 | memo2
----+----------------------------------+----------------------------------+-------
1 | c4ca4238a0b923820dcc509a6f75849b | c4ca4238a0b923820dcc509a6f75849b |
2 | c81e728d9d4c2f636f067f89cc14862c | c81e728d9d4c2f636f067f89cc14862c |
3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 |
4 | a87ff679a2f3e71d9181a67b7542122c | a87ff679a2f3e71d9181a67b7542122c |
5 | e4da3b7fbbce2345d7772b0674a318d5 | e4da3b7fbbce2345d7772b0674a318d5 |
(5 rows)
Time: 0.796 ms
postgres=# \d+ tmp_t4
Table "public.tmp_t4"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
--------+------------------------+-----------+----------+---------+----------+--------------+-------------
id | bigint | | | | plain | |
name | character varying(100) | | | | extended | |
memo1 | character varying(100) | | | | extended | |
memo2 | character varying(100) | | | | extended | |
postgres=# select oid,relname,relfilenode,relkind,relfrozenxid
from pg_class pc where pc.relname='tmp_t4';
oid | relname | relfilenode | relkind | relfrozenxid
--------+---------+-------------+---------+--------------
123886 | tmp_t4 | 123886 | r | 406624
(1 row)
Time: 0.579 ms
alter column set default
对列中不含null进行 set default 设置
postgres=# alter table tmp_t4 alter column memo1 set default 'aaa';
ALTER TABLE
Time: 1129.620 ms (00:01.130)
postgres=# \d+ tmp_t4
Table "public.tmp_t4"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
--------+------------------------+-----------+----------+--------------------------+----------+--------------+-------------
id | bigint | | | | plain | |
name | character varying(100) | | | | extended | |
memo1 | character varying(100) | | | 'aaa'::character varying | extended | |
memo2 | character varying(100) | | | | extended | |
postgres=# select oid,relname,relfilenode,relkind,relfrozenxid
from pg_class pc where pc.relname='tmp_t4';
oid | relname | relfilenode | relkind | relfrozenxid
--------+---------+-------------+---------+--------------
123886 | tmp_t4 | 123886 | r | 406624
(1 row)
Time: 0.443 ms
对列中含null进行 default 设置
postgres=# alter table tmp_t4 alter column memo2 set default 'aaa';
ALTER TABLE
Time: 128.971 ms
alter column drop default
postgres=# \d+ tmp_t4
Table "public.tmp_t4"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
--------+------------------------+-----------+----------+--------------------------+----------+--------------+-------------
id | bigint | | | | plain | |
name | character varying(100) | | | | extended | |
memo1 | character varying(100) | | | 'aaa'::character varying | extended | |
memo2 | character varying(100) | | | 'aaa'::character varying | extended | |
postgres=# alter table tmp_t4 alter column memo1 drop default;
ALTER TABLE
Time: 36.544 ms
postgres=# alter table tmp_t4 alter column memo2 drop default;
ALTER TABLE
Time: 59.798 ms
add column set default
postgres=# alter table tmp_t4 add column memo3 varchar(100) default 'aaa';
ALTER TABLE
Time: 73482.788 ms (01:13.483)
postgres=# select * from tmp_t4 limit 5;
id | name | memo1 | memo2 | memo3
----+----------------------------------+----------------------------------+-------+-------
1 | c4ca4238a0b923820dcc509a6f75849b | c4ca4238a0b923820dcc509a6f75849b | | aaa
2 | c81e728d9d4c2f636f067f89cc14862c | c81e728d9d4c2f636f067f89cc14862c | | aaa
3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 | | aaa
4 | a87ff679a2f3e71d9181a67b7542122c | a87ff679a2f3e71d9181a67b7542122c | | aaa
5 | e4da3b7fbbce2345d7772b0674a318d5 | e4da3b7fbbce2345d7772b0674a318d5 | | aaa
(5 rows)
Time: 0.619 ms
postgres=# select oid,relname,relfilenode,relkind,relfrozenxid
from pg_class pc where pc.relname='tmp_t4';
oid | relname | relfilenode | relkind | relfrozenxid
--------+---------+-------------+---------+--------------
123886 | tmp_t4 | 123894 | r | 406631
(1 row)
Time: 0.834 ms
relfilenode 由之前 123886 变为 123894
add column set default 确实要慎重
参考:
http://postgres.cn/docs/10/sql-altertable.html