我正在编写一些需要在数据库中存储项目的软件,这些项目需要具有“优先级”,因此我们最终会
ID | Name | Priority
--------+--------------+----------
1 | Pear | 4
2 | Apple | 2
3 | Orange | 1
4 | Banana | 3
所以现在,最重要的水果是橘子,然后是苹果,然后是香蕉,然后是梨。
现在,我想让Pear成为梨子,橘子,苹果,香蕉的首选。该表格如下:
ID | Name | Priority
--------+--------------+----------
1 | Pear | 1
2 | Apple | 3
3 | Orange | 2
4 | Banana | 4
使用PHP和Postgres实现这一目标的最佳方法是什么。鉴于该表不会超过大约12-13项,我已经考虑过选择整个表并在更新所有内容之前重写优先级。
*重要*
可以按任何顺序更改优先级,因此可以将优先级7设置为优先级3(从而将优先级低于优先级3的所有内容降低一级),并且我们需要缩小优先级为7的项目,该项目已移至优先级3已离开优先级列表。
答案 0 :(得分:1)
单个事务中的两个更新应该可以在这么小的表上正常工作。
create temp table priorities (
id integer primary key,
name varchar(15) not null,
priority integer not null check (priority > 0 and priority < 100)
);
insert into priorities values
(1,'Pear',4),
(2,'Apple',2),
(3,'Orange',1),
(4,'Banana',3);
-- Make Pear priority 1.
begin;
update priorities
set priority = priority + 1
-- The value below is the priority you're aiming for. You want
-- Pear to be #1, so you use ">= 1".
where priority >= 1;
update priorities
set priority = 1 where name = 'Pear';
commit;
为方便起见,您可以将其包装在存储过程中。
答案 1 :(得分:0)
好的,这是我尝试保持优先级的独特性和连续性。由触发器+功能实现。困难的部分是避免可能由触发器内的更新导致的无限递归。这是通过污垢/颜色标志解决的,必须将其放在桌子内。它的价值并不重要;只是改变它。
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;
CREATE TABLE fruits
( id INTEGER NOT NULL PRIMARY KEY
, zname varchar NOT NULL
, priority INTEGER NOT NULL
, flipflag boolean NOT NULL default false
, 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)
;
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 TRIGGER shift_priority
AFTER UPDATE OF priority ON fruits
FOR EACH ROW
WHEN (OLD.flipflag = NEW.flipflag AND OLD.priority <> NEW.priority)
EXECUTE PROCEDURE shift_priority()
;
UPDATE fruits
SET priority = 1
WHERE id=1;
结果:
SELECT * FROM fruits ORDER BY id;
NOTICE: drop cascades to 2 other objects
DETAIL: drop cascades to table tmp.fruits
drop cascades to function tmp.shift_priority()
DROP SCHEMA
CREATE SCHEMA
SET
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "fruits_pkey" for table "fruits"
NOTICE: CREATE TABLE / UNIQUE will create implicit index "unique_priority" for table "fruits"
CREATE TABLE
INSERT 0 4
CREATE FUNCTION
CREATE TRIGGER
UPDATE 1
id | zname | priority | flipflag
----+--------+----------+----------
1 | Pear | 1 | f
2 | Apple | 3 | t
3 | Orange | 2 | t
4 | Banana | 4 | t
(4 rows)