How to Concatenate Multiple Rows into a Single String Using GROUP_CONCAT and CONCAT in MySQL?

Using GROUP_CONCAT within CONCAT in MySQL

To concatenate multiple rows into a single string, while grouping them by common values, you can utilize the GROUP_CONCAT function. Let's explore its application with a practical example.

Question:

Given a table named mytbl with data as follows:

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

How can we transform this data into the following format:

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

Answer:

To achieve this, you can employ a combination of nested GROUP_CONCAT and CONCAT functions:

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;

Explanation:

• The innermost query groups the data by both id and Name, then concatenates the Value column with a comma as a separator for each group.
• The outer query groups the results by id and concatenates the previously concatenated Name strings, which now contain the values for each Name within each id.

This nested GROUP_CONCAT and CONCAT combination enables you to generate the desired output, where each id is associated with a comma-separated string of Name and their corresponding Value.

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