> ## Documentation Index > Fetch the complete documentation index at: https://villagesql.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # MySQL GROUP_CONCAT > How GROUP_CONCAT joins the values in a MySQL group into 1 string, how to sort and separate them, and the byte limit that truncates it with only a warning. All examples on this page work on VillageSQL. Install Now → `COUNT` tells you how many rows are in a group. `GROUP_CONCAT` tells you what they were, by joining their values into 1 string. It is the aggregate that keeps the detail instead of reducing it to a number. Open the client with `mysql -u root -p sakila` before you start. ## How GROUP\_CONCAT works ```sql theme={null} SELECT GROUPING_COLUMN, GROUP_CONCAT(COLUMN_NAME ORDER BY COLUMN_NAME SEPARATOR 'SEPARATOR_TEXT') FROM TABLE_NAME GROUP BY GROUPING_COLUMN; ``` Replace `GROUPING_COLUMN` with the column that defines the groups, `TABLE_NAME` with the table, `COLUMN_NAME` with the column to join, and `SEPARATOR_TEXT` with what goes between the values. Both `ORDER BY` and `SEPARATOR` are optional, and they live inside the brackets rather than in the query around them. Without `SEPARATOR` the values are joined with a comma and no space. Without `ORDER BY` they arrive in no particular order. ## Examples ### 1) Join the values in each group ```sql theme={null} SELECT rating, GROUP_CONCAT(title ORDER BY title SEPARATOR ', ') AS titles FROM film WHERE length = 185 GROUP BY rating ORDER BY rating; ``` ```text theme={null} +--------+--------------------------------------------------+ | rating | titles | +--------+--------------------------------------------------+ | G | CONTROL ANTHEM, DARN FORRESTER, MUSCLE BRIGHT | | PG | WORST BANGER | | PG-13 | CHICAGO NORTH, GANGS PRIDE, POND SEATTLE | | R | HOME PITY, SOLDIERS EVOLUTION, SWEET BROTHERHOOD | +--------+--------------------------------------------------+ 4 rows in set (0.00 sec) ``` 4 rows rather than 5, because no `NC-17` film runs 185 minutes and `WHERE` removed its rows before the grouping. A group with no rows left does not appear. ### 2) Drop the repeats `DISTINCT` inside the brackets removes duplicate values within each group. ```sql theme={null} SELECT rating, GROUP_CONCAT(DISTINCT rental_rate ORDER BY rental_rate) AS rates FROM film GROUP BY rating ORDER BY rating; ``` ```text theme={null} +--------+----------------+ | rating | rates | +--------+----------------+ | G | 0.99,2.99,4.99 | | PG | 0.99,2.99,4.99 | | PG-13 | 0.99,2.99,4.99 | | R | 0.99,2.99,4.99 | | NC-17 | 0.99,2.99,4.99 | +--------+----------------+ 5 rows in set (0.00 sec) ``` Without `DISTINCT` each string would hold 1 copy of the rate per film in the group, between 178 and 223 of them, and the 2 longest would run into the limit the next section is about. This is also the default separator: a comma and nothing else. ## The result is cut off at group\_concat\_max\_len bytes This is the trap. The server truncates a `GROUP_CONCAT` result that gets too long, and it does not raise an error. The limit is a setting, so the number below is this server's rather than a property of MySQL, and it counts bytes rather than characters. ```sql theme={null} SELECT LENGTH(GROUP_CONCAT(title)) AS bytes FROM film; ``` ```text theme={null} +-------+ | bytes | +-------+ | 1024 | +-------+ 1 row in set, 1 warning (0.00 sec) ``` Exactly 1,024, which is suspicious on its own: a real total would rarely land on a round number. Check it against the setting. ```sql theme={null} SELECT @@group_concat_max_len AS max_len; ``` ```text theme={null} +---------+ | max_len | +---------+ | 1024 | +---------+ 1 row in set (0.00 sec) ``` The footer of the first query reported a warning, and `SHOW WARNINGS` says what was lost: `Warning 1260 Row 65 was cut by GROUP_CONCAT()`. The string holds 64 whole titles out of 1,000 and then stops in the middle of the 65th. Run `SHOW WARNINGS` yourself after a `GROUP_CONCAT` to see the same message. `SET SESSION group_concat_max_len = 100000;` raises the limit for the rest of your connection and reverts when you reconnect. Because the limit counts bytes, text outside ASCII is cut sooner than the number suggests: a character can take up to 4 bytes in `utf8mb4`. Treat a result whose length equals `group_concat_max_len` exactly as truncated until you have checked, and watch the warning count in the footer. ## Summary * Use `GROUP_CONCAT` to join the values in a group into 1 string. * Put `ORDER BY`, `SEPARATOR` and `DISTINCT` inside the brackets. * Expect a comma with no space when you name no separator. * Expect truncation at `group_concat_max_len` bytes, with a warning rather than an error. * Suspect truncation whenever the length equals the limit exactly. ## See also * [Aggregate functions](/docs/tutorial/aggregate-functions) — the aggregates that return a number * [GROUP BY](/docs/tutorial/group-by) — building the groups this joins * [MySQL string functions](/docs/guides/string-functions) — reshaping the string afterwards * [MySQL GROUP BY performance](/docs/guides/group-by-having) — what building these strings costs at scale