How Can MySQL's GROUP_CONCAT and CONCAT Functions Transform Multiple Rows into a Single Comma-Separated String?

Utilizing GROUP_CONCAT and CONCAT for Data Transformation in MySQL

In MySQL, combining data from multiple rows into a single string can be achieved through the use of the GROUP_CONCAT function. Consider a table containing the following information:

id	Name	Value
1	A	4
1	A	5
1	B	8
2	C	9

An objective could be to transform this data into the following format:

id	Column
1	A:4,5,B:8
2	C:9

To accomplish this, a combined approach of GROUP_CONCAT and CONCAT can be employed. Here's the query:

select id, group_concat(`Name` separator ',') as `ColumnName`
from
(
  select id, 
  concat(`Name`, ':', group_concat(`Value` separator ',')) as Name
   from mytbl group by id, Name
) tbl
group by id;

This query operates in two stages:

1. It first groups by the id and Name columns, concatenating values within each group using the GROUP_CONCAT function. This produces a result set with unique pairs of id and Name where Value is provided in a comma-separated format.
2. The outer group by id operation further combines the results of the inner query, resulting in a single row for each unique id with a comma-separated list of Name:Value pairs.

By executing this query, you will obtain the desired data transformation, with rows in the following format:

id	Column
1	A:4,5,B:8
2	C:9

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