create table region(

    id serial PRIMARY KEY,

    name character varying(128),

    value smallint default 8

);

#会自动创建 region_seq_id表,drop表region时，会自动将region_seq_id表drop

# 删除表中的所有行,并使主键重新计数

truncate region restart identity;

# 或者设置下一条sql插入时的技术起始值

select setval('region_seq_id', 1, false)

create table user (

    id serial primary key,

    reg_id integer references region(id),

    name character varying(128)

);

# 或者

create table user (

    id serial primary key,

    reg_id integer,

    name character varying(128),

    forien key(reg_id) references region(id)

);

# 添加列

alter table region add column description text;

# 移除列

alter table region drop column description;

# 修改列上的默认值

alter table region alter column value set default 0;

# 移除列的默认值

alter table region alter column value drop default;

# 修改列的数据类型

alter table region alter column value type interger;

# 列重命名

alter table region rename column value to region_time;

# 表重命名

alter table region rename to region_time;