金仓数据库KingbaseES之自增列
关键字：自增列，sequence，serial，identity
KingbaseES中一共3种自增长类型sequence，serial，identity，他们的区别如下表：
| 对象 |
sequence | serial | identity |
| 显示插入 | 是 | 是 | 是 |
| 显示插入后更新最大值 | 否 | 否 | 否 |
| 清空表后是否重置 | 否 | 否 | 否 |
| 是否跟事务一起回滚 | 否 | 否 | 否 |
| 多对象共享 | 是 | 否 | 否 |
| 支持重置 | 是 | 是 | 是 |
| 出现错误后序列值是否增长 | 是 | 是 | 是 |
-
Sequence
测试用例：
create sequence seq_1 INCREMENT BY 1 MINVALUE 1 START WITH 1;
create table test_seq
(
id int not null default nextval('seq_1') primary key,
name varchar(10)
);隐式插入：
insert into test_seq (name) values ('aaa');
insert into test_seq (name) values ('bbb');
insert into test_seq (name) values ('ccc');显式插入：
insert into test_seq (id,name) values (5,'ddd');
select * from test_seq;查询结果
test1=# select * from test_seq;
id | name
----+------
1 | aaa
2 | bbb
3 | ccc
5 | ddd再次隐式插入
--可以正常插入
insert into test_seq (name) values ('eee');--插入失败，主键重复，因为序列自身是递增的，不会关心表中被显式插入的数据
insert into test_seq (name) values ('fff');
test1=# insert into test_seq (name) values ('eee');
INSERT 0 1
test1=# insert into test_seq (name) values ('fff');
错误: 重复键违反唯一约束"test_seq_pkey"
描述: 键值"(id)=(5)" 已经存在--再次执行语句可正常插入，序列因为之前的错误调用自动增加
test1=# insert into test_seq (name) values ('fff');
INSERT 0 1
test1=# select * from test_seq;
id | name
----+------
1 | aaa
2 | bbb
3 | ccc
5 | ddd
4 | eee
6 | fff--重置序列的最大值
select setval(' seq_1',(select max(id) from test_seq)::BIGINT);--事务回滚后，序列号并不会回滚
test1=# begin;
BEGIN
test1=# insert into test_seq (name) values ('ggg');
INSERT 0 1
test1=# rollback;
ROLLBACK
test1=#
test1=#
test1=# select * from test_seq;
id | name
----+------
1 | aaa
2 | bbb
3 | ccc
5 | ddd
4 | eee
6 | fff
(6 行记录)
test1=# insert into test_seq (name) values ('ggg');
INSERT 0 1
test1=# select * from test_seq;
id | name
----+------
1 | aaa
2 | bbb
3 | ccc
5 | ddd
4 | eee
6 | fff
8 | ggg
(7 行记录)-- truncate 表之后，序列不受影响
test1=# truncate table test_seq;
TRUNCATE TABLE
test1=# insert into test_seq (name) values ('ggg');
INSERT 0 1
test1=# select * from test_seq;
id | name
----+------
9 | ggg
(1 行记录)--重置序列
ALTER SEQUENCE seq_1 RESTART WITH 1;
test1=# ALTER SEQUENCE seq_1 RESTART WITH 1;
ALTER SEQUENCE
test1=# insert into test_seq (name) values ('ggg');
INSERT 0 1
test1=# select * from test_seq;
id | name
----+------
9 | ggg
1 | ggg-
Serial
测试用例
create table test_serial
(
id serial primary key,
name varchar(100)
);隐式插入
insert into test_serial(name) values ('aaa');
insert into test_serial(name) values ('bbb');
insert into test_serial(name) values ('ccc');显示插入
insert into test_serial(id,name) values (5,'ddd);
select * from test_serial;--再次隐式插入,第二次会报错
insert into test_serial(name) values ('eee');
insert into test_serial(name) values ('fff');
test1=# insert into test_serial(id,name) values (5,'ddd);
INSERT 0 1
test1=# insert into test_serial(name) values ('eee');
INSERT 0 1
test1=# insert into test_serial(name) values ('fff');
错误: 重复键违反唯一约束"test_serial_pkey"
描述: 键值"(id)=(5)" 已经存在--再次执行语句可正常插入，序列因为之前的错误调用自动增加
test1=# insert into test_serial(name) values ('fff');
INSERT 0 1
test1=# select * from test_serial;
id | name
----+------
1 | aaa
2 | bbb
3 | ccc
5 | ddd
4 | eee
6 | fff
(6 行记录)--重置serial
SELECT SETVAL((SELECT sys_get_serial_sequence(' test_serial', 'id')), 1, false);-
Identity
Identity是R6版本新增的语法，R3数据库不支持该语法。
identity定义成generated by default as identity允许显式插入，
identity定义成always as identity 不允许显示插入，但是加上overriding system value也可以显式插入。
测试用例1：
create table test_identiy_1
(
id int generated always as identity (START WITH 1 INCREMENT BY 1) primary key ,
name varchar(100)
);
insert into test_identiy_1(name) values ('aaa');
insert into test_identiy_1(name) values ('bbb');
insert into test_identiy_1(name) values ('ccc');显式插入值
如果定义为generated always as identity则不允许显式插入，除非增加overriding system value 提示。
insert into test_identiy_1(id,name) values (5,'ccc');
insert into test_identiy_1(id,name)overriding system value values (5,'ccc');
test1=# insert into test_identiy_1(id,name) values (5,'ccc');
错误: 无法插入到列"id"
描述: 列"id"是定义为GENERATED ALWAYS的标识列.
提示: 使用OVERRIDING SYSTEM VALUE覆盖.
test1=# insert into test_identiy_1(id,name)overriding system value values (5,'ccc');
INSERT 0 1测试用例2：
create table test_identiy_2
(
id int generated by default as identity (START WITH 1 INCREMENT BY 1) primary key ,
name varchar(100)
);
insert into test_identiy_2(name) values ('aaa');
insert into test_identiy_2(name) values ('bbb');
insert into test_identiy_2(name) values ('ccc');
test1=# insert into test_identiy_2(id,name) values (5,'ccc');
INSERT 0 1重置Identity的方式有2种：
--方式1：
ALTER TABLE test_identiy_1 ALTER COLUMN id RESTART WITH 100;
--方式2：
TRUNCATE table test_identiy_1 RESTART IDENTITY;