os: centos 7.4
db: postgresql 10.11

創建表后，有時需要對表進行 set default 或者 drop default 設置。

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 mspostgres=# create table tmp_t4( id int8, name varchar(100), memo1 varchar(100), memo2 varchar(100) ); CREATE TABLE Time: 360.530 mspostgres=# 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 mspostgres=# \d+ tmp_t4Table "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

對列中不含null進行 set default 設置

postgres=# alter table tmp_t4 alter column memo1 set default 'aaa'; ALTER TABLE Time: 1129.620 ms (00:01.130)postgres=# \d+ tmp_t4Table "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

對列中含null進行 default 設置

postgres=# alter table tmp_t4 alter column memo2 set default 'aaa'; ALTER TABLE Time: 128.971 ms

alter column drop default

postgres=# \d+ tmp_t4Table "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 | | aaa2 | c81e728d9d4c2f636f067f89cc14862c | c81e728d9d4c2f636f067f89cc14862c | | aaa3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 | eccbc87e4b5ce2fe28308fd9f2a7baf3 | | aaa4 | a87ff679a2f3e71d9181a67b7542122c | a87ff679a2f3e71d9181a67b7542122c | | aaa5 | e4da3b7fbbce2345d7772b0674a318d5 | e4da3b7fbbce2345d7772b0674a318d5 | | aaa (5 rows)Time: 0.619 mspostgres=# 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 變為 123894

add column set default 確實要慎重

參考:
http://postgres.cn/docs/10/sql-altertable.html

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