How Can I Concatenate Multiple MySQL Rows into a Single Field?

Combining Multiple MySQL Rows into One Field

MySQL joins often return many rows, making data analysis cumbersome. This article shows how to efficiently combine multiple rows into a single field for easier handling.

The GROUP_CONCAT function is key to this process. For example:

SELECT person_id,
       GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

This query groups hobbies by person_id, concatenating them with commas as separators.

To remove duplicates, use DISTINCT:

SELECT person_id,
       GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

For sorted results, use ORDER BY:

SELECT person_id,
       GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

Remember, GROUP_CONCAT has a default 1024-byte limit. To increase this, use:

SET group_concat_max_len = 2048;

Or, dynamically calculate the required length:

SET group_concat_max_len = CAST(
                     (SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
                           FROM peoples_hobbies
                           GROUP BY person_id) AS UNSIGNED);

GROUP_CONCAT simplifies data manipulation by consolidating multiple rows into a single, more manageable field.

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