MySQL将行值与逗号等结合 [英] MySQL Combine row values with comma and more

问题描述

一段时间以来，我一直在head头。主要不是要获得解决方案，而要如何运作。

I have been banging my head over this for a while. Mainly it's not about getting a solution BUT how it works. It would be great if you can give explanation on how the solution is implemented.

这只是示例数据，我正在处理5个带有内联SELECT语句的表。谢谢SQL Gurus。

This is just sample data, I am working with 5 tables with inline SELECT statements. Thank you SQL Gurus.

CREATE TABLE source
(
  product varchar(20),
  amount decimal
)

CREATE TABLE cat
(
  category varchar(20),
  product varchar(20)
)

插入样本数据：

Insert Sample Data:

INSERT INTO source (product, amount) VALUES
('product1', 1.00),
('product2', 2.00),
('product3', 1.50),
('product4', 5.25)

INSERT INTO cat (category, product) VALUES
('Shirts', 'product1'),
('Green Shirt', 'product1'),
('Gadget', 'product1'),
('Food', 'product2'),
('Games', 'product4')

我的试用查询：

My Trial Query:

DECLARE @categories varchar(200)
SET @categories = NULL

SELECT 
@categories = COALESCE(@categories + ',','') + cat.category
FROM cat

SELECT
DISTINCT source.product,
@categories
FROM cat
JOIN source on source.product = cat.product

输出

OUTPUT

PRODUCT     COLUMN_1
product1    Shirts,Green Shirt,Gadget,Food,Games
product2    Shirts,Green Shirt,Gadget,Food,Games
product4    Shirts,Green Shirt,Gadget,Food,Games

期望的输出：

DESIRED OUTPUT:

PRODUCT     COLUMN_1
product1    Shirts, Green Shirt, Gadget
product2    Gadget, Food
product4    Games

推荐答案

我认为这就是您要使用的东西 GROUP_CONCAT ：

I think this is what you're looking for using GROUP_CONCAT:

SELECT
  source.product,
  GROUP_CONCAT(cat.category) cats
FROM cat
  JOIN source on source.product = cat.product
GROUP BY source.product

SQL小提琴演示

如果您尝试在'bewe'中获取'，'在每个类别中，将 SEPARATOR 与 GROUP_CONCAT 结合使用。例如：

If you're trying to get a ', ' in between each category, use SEPARATOR with GROUP_CONCAT. For example:

GROUP_CONCAT(cat.category separator ', ')

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