How to Combine GROUP_CONCAT and CONCAT for Complex Data Aggregation in MySQL?

How to Use GROUP_CONCAT in a CONCAT in MySQL

In certain scenarios, you may encounter the need to transform data stored in a MySQL table into a specific format. For instance, suppose you have a table with data like this:

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

Your goal is to obtain the following results:

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

To achieve this transformation, you'll need to utilize the GROUP_CONCAT() function. This function stands out in its ability to concatenate values from multiple rows, grouped by certain criteria.

To begin, you'll need to generate a subquery that concatenates the values grouped by both id and Name. The following code snippet demonstrates this step:

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

The resulting subquery will create a new column called Name that includes all values concatenated by colons and commas, grouped by both id and Name.

| id | Name |
| --- | ---- |
| 1 | A:4,5 |
| 1 | B:8 |
| 2 | C:9 |

Finally, apply GROUP_CONCAT() again to the outermost query, this time using id as the grouping criteria. This step will concatenate the Name values from the subquery, separated by commas:

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;

The result will be exactly as desired:

| id | Column |
| --- | ----- |
| 1 | A:4,5,B:8 |

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