每组值定制SERIAL /自动增量

本文介绍了每组值定制SERIAL /自动增量的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

简单来说，我的文章表：

id SERIAL， category VARCHAR FK， category_id INT

id 列显然是PK它被用作所有文章的全局标识符。

类别列是好的..类别。 p>

category_id 用作类别中的 UNIQUE ID目前有一个 UNIQUE（category，category_id）约束。

然而，我也想要code> category_id to auto-increment 。

我想要这样，每次执行查询像

INSERT INTO文章（category）VALUES（'stackoverflow'）;

我希望 category_id 列自动根据stackoverflow类别的最新 category_id 填写。

在我的逻辑代码中实现这一点简单。我只是选择最新的num并插入+1，但涉及两个单独的查询。 我正在寻找可以在一个查询中执行所有这一切的SQL解决方案。

解决方案

概念

至少有几种方法可以解决这个问题。首先，我想到：

在为每行执行的触发器中为 category_id 列分配一个值，

动作 通过覆盖 INSERT 语句的输入值

这是 SQL小提琴 查看代码在行动

对于一个简单的测试，我正在创建文章表格持有类别及其 id ，它们对于每个类别应该是唯一的。我已经省略了约束创建 - 这与提出的点无关。

创建表文章（id serial，category varchar，category_id int ）

使用 generate_series（）函数具有自动增量已经存在。

插入文章（category，category_id） select'stackoverflow'，我来自generate_series（1,1）i union all select'stackexchange'，我来自generate_series（1,3）i

创建一个触发器函数，它将选择 MAX（category_id）并将其值增加 1 对于类别我们正在插入一行，然后覆盖该值，然后再继续使用实际的 INSERT 到表（ BEFORE INSERT 触发器处理）。

创建或替换功能category_increment（） RETURNS触发器 LANGUAGE plpgsql AS $$ DECLARE v_category_inc int：= 0; BEGIN SELECT MAX（category_id）+ 1 INTO v_category_inc FROM article WHERE category = NEW.category; 如果v_category_inc为空THEN NEW.category_id = 1; ELSE NEW.category_id：= v_category_inc; END IF; 返回新; END; $$

使用该功能作为触发器。

CREATE TRIGGER trg_category_increment BEFORE INSERT ON文章为每个ROW执行程序category_increment（）

为现有的类别和不存在的类别插入一些值（后触发器）。

INSERT INTO文章（category）VALUES （'stackoverflow'），（'stackexchange'） ，（'nonexisting'）;

查询用于选择数据：

选择类别，category_id从文章顺序1,2

初始插入的结果：

category category_id stackexchange 1 stackexchange 2 stackexchange 3 stackoverflow 1

最终插入后的结果：

category category_id nonexisting 1 stackexchange 1 stackexchange 2 stackexchange 3 stackexchange 4 stackoverflow 1 stackoverflow 2

I'm trying to make a blog system of sort and I ran into a slight problem.

Simply put, there's 3 columns in my article table:

id SERIAL, category VARCHAR FK, category_id INT

id column is obviously the PK and it is used as a global identifier for all articles.

category column is well .. category.

category_id is used as a UNIQUE ID within a category so currently there is a UNIQUE(category, category_id) constraint in place.

However, I also want for category_id to auto-increment.

I want it so that every time I execute a query like

INSERT INTO article(category) VALUES ('stackoverflow');

I want the category_id column to be automatically be filled according to the latest category_id of the 'stackoverflow' category.

Achieving this in my logic code is quite easy. I just select latest num and insert +1 of that but that involves two separate queries. I am looking for a SQL solution that can do all this in one query.

解决方案

Concept

There are at least several ways to approach this. First one that comes to my mind:

Assign a value for category_id column inside a trigger executed for each row, by overwriting the input value from INSERT statement.

Action

Here's the SQL Fiddle to see the code in action

For a simple test, I'm creating article table holding categories and their id's that should be unique for each category. I have omitted constraint creation - that's not relevant to present the point.

create table article ( id serial, category varchar, category_id int )

Inserting some values for two distinct categories using generate_series() function to have an auto-increment already in place.

insert into article(category, category_id) select 'stackoverflow', i from generate_series(1,1) i union all select 'stackexchange', i from generate_series(1,3) i

Creating a trigger function, that would select MAX(category_id) and increment its value by 1 for a category we're inserting a row with and then overwrite the value right before moving on with the actual INSERT to table (BEFORE INSERT trigger takes care of that).

CREATE OR REPLACE FUNCTION category_increment() RETURNS trigger LANGUAGE plpgsql AS $$ DECLARE v_category_inc int := 0; BEGIN SELECT MAX(category_id) + 1 INTO v_category_inc FROM article WHERE category = NEW.category; IF v_category_inc is null THEN NEW.category_id := 1; ELSE NEW.category_id := v_category_inc; END IF; RETURN NEW; END; $$

Using the function as a trigger.

CREATE TRIGGER trg_category_increment BEFORE INSERT ON article FOR EACH ROW EXECUTE PROCEDURE category_increment()

Inserting some more values (post trigger appliance) for already existing categories and non-existing ones.

INSERT INTO article(category) VALUES ('stackoverflow'), ('stackexchange'), ('nonexisting');

Query used to select data:

select category, category_id From article order by 1,2

Result for initial inserts:

category category_id stackexchange 1 stackexchange 2 stackexchange 3 stackoverflow 1

Result after final inserts:

category category_id nonexisting 1 stackexchange 1 stackexchange 2 stackexchange 3 stackexchange 4 stackoverflow 1 stackoverflow 2