如何在一个列中得到连续递增的数字，且不缺失任何数字？

Question

如何在一个列中得到连续递增的数字，且不缺失任何数字？

8

我想问一下，在PostgreSQL中是否存在这样的可能性：如果我有5行数据，并且在其中一列中有数字“1, 2, 3, 4, 5”，并且该列不是主键，如果我删除第三行，那么PostgreSQL是否会重新对该列进行编号，以便我可以得到“1, 2, 3, 4”而不是“1, 2, 4, 5”？
Possible Duplicates:
如何在PostgreSQL查询中显示行号？
使用Postgresql重新排序带有标识符的列
使用子选择更新PostgreSQL记录顺序

- Wine Too

1个回答

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- wildplasser · Accepted Answer

这篇文章是基于之前的回答进行适应而来。当应用程序需要变量(即EAV模型中的记录)的标签顺序（也可以是备选键的一部分）时，这种情况经常发生。

priority字段需要保持连续，这就是所谓的"标签顺序"
在插入时: 所有优先级大于等于新记录的记录应该增加他们的优先级
类似地，在删除时：减小优先级
如果一条记录的优先级被更新，那么在旧的和新的优先级值之间的记录应该将它们的优先级上移或下移。
为了避免递归触发器调用：
- 触发器更新翻转任何记录的翻转标志。
- 并测试old.flipflag=new.flipflag以检测真正的更新（不是由触发器引起的那些更新）。

        -- Make some data
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;

CREATE TABLE fruits
        ( id INTEGER NOT NULL PRIMARY KEY
        , priority INTEGER NOT NULL
        , flipflag boolean NOT NULL default false
        , zname varchar NOT NULL
        , CONSTRAINT unique_priority UNIQUE (priority) DEFERRABLE INITIALLY DEFERRED
        );
INSERT INTO fruits(id,zname,priority) VALUES
 (1  , 'Pear' ,4)
,(2  , 'Apple' ,2)
,(3  , 'Orange' ,1)
,(4  , 'Banana' ,3)
,(5  , 'Peach' ,5)
        ;

        -- Trigger functions for Insert/update/delete
CREATE function shift_priority()
RETURNS TRIGGER AS $body$

BEGIN
        UPDATE fruits fr
        SET priority = priority +1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE NEW.priority < OLD.priority
        AND OLD.flipflag = NEW.flipflag -- redundant condition
        AND fr.priority >= NEW.priority
        AND fr.priority < OLD.priority
        AND fr.id <> NEW.id             -- exlude the initiating row
                ;
        UPDATE fruits fr
        SET priority = priority -1
        , flipflag = NOT flipflag
        WHERE NEW.priority > OLD.priority
        AND OLD.flipflag = NEW.flipflag
        AND fr.priority <= NEW.priority
        AND fr.priority > OLD.priority
        AND fr.id <> NEW.id
        ;
        RETURN NEW;
END;

$body$
language plpgsql;

CREATE function shift_down_priority()
RETURNS TRIGGER AS $body$

BEGIN

        UPDATE fruits fr
        SET priority = priority -1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE fr.priority > OLD.priority
                ;
        RETURN NEW;
END;

$body$
language plpgsql;

CREATE function shift_up_priority()
RETURNS TRIGGER AS $body$

BEGIN
        UPDATE fruits fr
        SET priority = priority +1
        , flipflag = NOT flipflag       -- alternating bit protocol ;-)
        WHERE fr.priority >= NEW.priority
                ;
        RETURN NEW;
END;

$body$
language plpgsql;

        -- Triggers for Insert/Update/Delete
CREATE TRIGGER shift_priority_u
        AFTER UPDATE OF priority ON fruits
        FOR EACH ROW
        WHEN (OLD.flipflag = NEW.flipflag AND OLD.priority <> NEW.priority)
        EXECUTE PROCEDURE shift_priority()
        ;
CREATE TRIGGER shift_priority_d
        AFTER DELETE ON fruits
        FOR EACH ROW
        EXECUTE PROCEDURE shift_down_priority()
        ;
CREATE TRIGGER shift_priority_i
        BEFORE INSERT ON fruits
        FOR EACH ROW
        EXECUTE PROCEDURE shift_up_priority()
        ;

        -- Do some I/U/D operations
\echo Pears are Okay
UPDATE fruits
SET priority = 1
WHERE id=1; -- 1,4

SELECT * FROM fruits ORDER BY priority;

\echo dont want bananas
DELETE FROM fruits WHERE id = 4;
SELECT * FROM fruits ORDER BY priority;

\echo  We want Kiwis
INSERT INTO fruits(id,zname,priority) VALUES (4  , 'Kiwi' ,3) ;
SELECT * FROM fruits ORDER BY priority;

结果：

Pears are Okay
UPDATE 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  2 |        3 | t        | Apple
  4 |        4 | t        | Banana
  5 |        5 | f        | Peach
(5 rows)

dont want bananas
DELETE 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  2 |        3 | t        | Apple
  5 |        4 | t        | Peach
(4 rows)

We want Kiwis
INSERT 0 1
 id | priority | flipflag | zname  
----+----------+----------+--------
  1 |        1 | f        | Pear
  3 |        2 | t        | Orange
  4 |        3 | f        | Kiwi
  2 |        4 | f        | Apple
  5 |        5 | f        | Peach
(5 rows)