pg学习_基本表定义_修改表结构

修改表结构
1、增加字段
highgo=# \d test1
Table "public.test1"
Column |       Type        | Modifiers
--------+-------------------+-----------
id     | integer           |
name   | character varying |

highgo=# alter table test1 add addr varchar(20);
ALTER TABLE
highgo=# \d test1
Table "public.test1"
Column |         Type          | Modifiers
--------+-----------------------+-----------
id     | integer               |
name   | character varying     |
addr   | character varying(20) |

2、删除字段
highgo=# alter table test1 drop column addr;
ALTER TABLE
highgo=# \d test1
Table "public.test1"
Column |       Type        | Modifiers
--------+-------------------+-----------
id     | integer           |
name   | character varying |

3、修改字段
最好的方法
先建一个临时的表，然后删除该表，再创建新表，最后从临时表把记录导入进去。
highgo=# create table test6 (num int,name varchar(10),sex varchar(1) check(sex in('y','n')));
CREATE TABLE
highgo=# insert into test6 values(1,'aaa','y');
INSERT 0 1
highgo=#  insert into test6 values(2,'bbb','n');
INSERT 0 1
highgo=# create table test7
highgo-# as
highgo-# select * from test6;
SELECT 2
highgo=# drop table test6;
DROP TABLE
highgo=# create table test6(
highgo(# num int,
highgo(# name varchar(16),
highgo(# sex varchar(1) check(sex in('y','n')));
CREATE TABLE
highgo=# insert into test6
highgo-# select * from test7;
INSERT 0 2
highgo=# select * from test6;
num | name | sex
-----+------+-----
1 | aaa  | y
2 | bbb  | n
(2 rows)