可以说我有一张桌子:
Column | Type | Notes
---------+------------ +----------------------------------------------------------
id | integer | An ID that's FK to some other table
seq | integer | Each ID gets its own seq number
data | text | Just some text, totally irrelevant.
id
+ seq
是一个组合键。
我想看到的是:
ID | SEQ | DATA
----+------ +----------------------------------------------
1 | 1 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
1 | 2 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
1 | 3 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
1 | 4 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
2 | 1 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
3 | 1 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
3 | 2 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
3 | 3 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
3 | 4 | Quick brown fox, lorem ipsum, lazy dog, etc etc.
如您所见,id
和seq
的组合是独一无二的。
我不知道如何设置我的表(或插入语句?)来做到这一点。我想插入id
和data
,导致seq
是依赖于id
的子序列。
没问题!我们要制作两张桌子,things
和stuff
。 stuff
将是您在问题中描述的表格,things
就是它所指的那个:
CREATE TABLE things (
id serial primary key,
name text
);
CREATE TABLE stuff (
id integer references things,
seq integer NOT NULL,
notes text,
primary key (id, seq)
);
然后我们将使用触发器设置things
,每次创建一行时都会创建一个新序列:
CREATE FUNCTION make_thing_seq() RETURNS trigger
LANGUAGE plpgsql
AS $$
begin
execute format('create sequence thing_seq_%s', NEW.id);
return NEW;
end
$$;
CREATE TRIGGER make_thing_seq AFTER INSERT ON things FOR EACH ROW EXECUTE PROCEDURE make_thing_seq();
现在我们最终会得到thing_seq_1
,thing_seq_2
等等...
现在是stuff
的另一个触发器,每次都使用正确的序列:
CREATE FUNCTION fill_in_stuff_seq() RETURNS trigger
LANGUAGE plpgsql
AS $$
begin
NEW.seq := nextval('thing_seq_' || NEW.id);
RETURN NEW;
end
$$;
CREATE TRIGGER fill_in_stuff_seq BEFORE INSERT ON stuff FOR EACH ROW EXECUTE PROCEDURE fill_in_stuff_seq();
这将确保当行进入stuff
时,id
列用于找到调用nextval
的正确序列。
这是一个演示:
test=# insert into things (name) values ('Joe');
INSERT 0 1
test=# insert into things (name) values ('Bob');
INSERT 0 1
test=# select * from things;
id | name
----+------
1 | Joe
2 | Bob
(2 rows)
test=# \d
List of relations
Schema | Name | Type | Owner
--------+---------------+----------+----------
public | stuff | table | jkominek
public | thing_seq_1 | sequence | jkominek
public | thing_seq_2 | sequence | jkominek
public | things | table | jkominek
public | things_id_seq | sequence | jkominek
(5 rows)
test=# insert into stuff (id, notes) values (1, 'Keychain');
INSERT 0 1
test=# insert into stuff (id, notes) values (1, 'Pet goat');
INSERT 0 1
test=# insert into stuff (id, notes) values (2, 'Family photo');
INSERT 0 1
test=# insert into stuff (id, notes) values (1, 'Redundant lawnmower');
INSERT 0 1
test=# select * from stuff;
id | seq | notes
----+-----+---------------------
1 | 1 | Keychain
1 | 2 | Pet goat
2 | 1 | Family photo
1 | 3 | Redundant lawnmower
(4 rows)
test=#
您可以使用window function分配您的SEQ
值,例如:
INSERT INTO YourTable
(ID, SEQ, DATA)
SELECT ID, ROW_NUMBER() OVER(PARTITION BY ID ORDER BY DATA), DATA
FROM YourSource
如果seq
反映(或应该反映)插入行的顺序,我宁愿使用自动填充的timestamp
,并在使用row_number()
选择行时动态生成序列号:
create table some_table
(
id integer not null,
inserted_at timestamp not null default current_timestamp,
data text
);
要获得seq
列,您可以这样做:
select id,
row_number() over (partition by id order by inserted_at) as seq,
data
from some_table
order by id, seq;
然而,与使用持久化seq
列(特别是id, seq
上的索引)相比,select会慢一点。
如果这成为一个问题,您可以查看使用物化视图,或添加seq
列,然后定期更新它(出于性能原因,我不会在触发器中执行此操作)。
SQLFiddle示例:http://sqlfiddle.com/#!15/db69b/1
只是一个猜测。
INSERT INTO TABLE (ID, SEQ, DATA)
VALUES
(
IDVALUE,
(SELECT max(SEQ) +1 FROM TABLE WHERE ID = IDVALUU),
DATAVALUE
);
这是使用标准SQL的简单方法:
INSERT INTO mytable (id, seq, data)
SELECT << your desired ID >>,
COUNT(*) + 1,
'Quick brown fox, lorem ipsum, lazy dog, etc etc.'
FROM mytable
WHERE id = << your desired ID (same as above) >>;
(如果你想要有点聪明,你可以考虑创建一个trigger来在插入后立即使用相同的方法更新行。)
我有同样需要动态存储树状结构,而不是一次添加所有ID。 我不喜欢为每个组使用序列表,因为它们可能有数千个。 它运行在密集的多处理环境中,因此必须具有竞争条件。 这里是第1级的插入功能。其他级别遵循相同的原则。
每个组作为独立的不可重复使用的顺序ID,该功能接收组名和子组名,为您提供现有ID或创建它并返回新ID。 我尝试了一个循环来进行单个选择,但是代码的长度和难度都很大。
CREATE OR REPLACE FUNCTION getOrInsert(myGroupName TEXT, mySubGroupName TEXT)
RETURNS INT AS
$BODY$
DECLARE
myId INT;
BEGIN -- 1st try to get it if it already exists
SELECT id INTO myId FROM myTable
WHERE groupName=myGroupName AND subGroupName=mySubGroupName;
IF NOT FOUND THEN
-- Only 1 session can get it but others can read
LOCK TABLE myTable IN SHARE ROW EXCLUSIVE MODE;
-- 2nd try in case of race condition
SELECT id INTO myId FROM myTable
WHERE groupName=myGroupName AND subGroupName=mySubGroupName;
IF NOT FOUND THEN -- Doesn't exist. Get next ID for this group.
SELECT COALESCE(MAX(id), 0)+1 INTO myId FROM myTable
WHERE groupName=myGroupName;
INSERT INTO myTable (groupName, id, subGroupName)
VALUES (myGroupName, myId, mySubGroupName);
END IF;
END IF;
RETURN myId;
END;
$BODY$
LANGUAGE plpgsql VOLATILE COST 100;
尝试一下:
CREATE TABLE myTable (GroupName TEXT, SubGroupName TEXT, id INT);
SELECT getOrInsert('groupA', 'subgroupX'); -- Returns 1
...
SELECT * FROM myTable;
groupname | subgroupname | id
-----------+--------------+----
groupA | subgroupX | 1
groupA | subgroupY | 2
groupA | subgroupZ | 3
groupB | subgroupY | 1
PostgreSQL支持分组的唯一列,如下所示:
CREATE TABLE example (
a integer,
b integer,
c integer,
UNIQUE (a, c)
);
见PostgreSQL Documentation - 第5.3.3节
简单 :-)
我没有任何postgresql特定的经验,但你可以在insert语句中使用子查询吗?在Mysqlish中,
INSERT INTO MYTABLE SET
ID=4,
SEQ=( SELECT MAX(SEQ)+1 FROM MYTABLE WHERE ID=4 ),
DATA="Quick brown fox, lorem ipsum, lazy dog, etc etc."