PostgreSQL序列基于另一列

问题描述 投票:36回答:9

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,idseq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iddata,导致seq是依赖于id的子序列。

sql postgresql
9个回答
20
投票

没问题!我们要制作两张桌子,thingsstuffstuff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_1thing_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=#

16
投票

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

4
投票

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


0
投票

只是一个猜测。

INSERT INTO TABLE (ID, SEQ, DATA)
VALUES
(
 IDVALUE,
 (SELECT max(SEQ) +1 FROM TABLE WHERE ID = IDVALUU),
 DATAVALUE
);

0
投票

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) >>;

SQL Fiddle Demo

(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。)


0
投票

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

-1
投票

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)
);

PostgreSQL Documentation - 第5.3.3节

简单 :-)


-2
投票

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."
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