How to make a subquery column MYSQL [duplicate] - mysql

Question

Using MySQL, I can do something like:
SELECT hobbies FROM peoples_hobbies WHERE person_id = 5;
My Output:
shopping
fishing
coding
but instead I just want 1 row, 1 col:
Expected Output:
shopping, fishing, coding
The reason is that I'm selecting multiple values from multiple tables, and after all the joins I've got a lot more rows than I'd like.
I've looked for a function on MySQL Doc and it doesn't look like the CONCAT or CONCAT_WS functions accept result sets.
So does anyone here know how to do this?

Answer 1

You can use GROUP_CONCAT:
SELECT person_id,
GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Ludwig stated in his comment, you can add the DISTINCT operator to avoid duplicates:
SELECT person_id,
GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Jan stated in their comment, you can also sort the values before imploding it using ORDER BY:
SELECT person_id,
GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;
As Dag stated in his comment, there is a 1024 byte limit on the result. To solve this, run this query before your query:
SET group_concat_max_len = 2048;
Of course, you can change 2048 according to your needs. To calculate and assign the value:
SET group_concat_max_len = CAST(
(SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
FROM peoples_hobbies
GROUP BY person_id) AS UNSIGNED);

Answer 2

Have a look at GROUP_CONCAT if your MySQL version (4.1) supports it. See the documentation for more details.
It would look something like:
SELECT GROUP_CONCAT(hobbies SEPARATOR ', ')
FROM peoples_hobbies
WHERE person_id = 5
GROUP BY 'all';

Answer 3

Alternate syntax to concatenate multiple, individual rows
WARNING: This post will make you hungry.
Given:
I found myself wanting to select multiple, individual rows—instead of a group—and concatenate on a certain field.
Let's say you have a table of product ids and their names and prices:
+------------+--------------------+-------+
| product_id | name | price |
+------------+--------------------+-------+
| 13 | Double Double | 5 |
| 14 | Neapolitan Shake | 2 |
| 15 | Animal Style Fries | 3 |
| 16 | Root Beer | 2 |
| 17 | Lame T-Shirt | 15 |
+------------+--------------------+-------+
Then you have some fancy-schmancy ajax that lists these puppies off as checkboxes.
Your hungry-hippo user selects 13, 15, 16. No dessert for her today...
Find:
A way to summarize your user's order in one line, with pure mysql.
Solution:
Use GROUP_CONCAT with the the IN clause:
mysql> SELECT GROUP_CONCAT(name SEPARATOR ' + ') AS order_summary FROM product WHERE product_id IN (13, 15, 16);
Which outputs:
+------------------------------------------------+
| order_summary |
+------------------------------------------------+
| Double Double + Animal Style Fries + Root Beer |
+------------------------------------------------+
Bonus Solution:
If you want the total price too, toss in SUM():
mysql> SELECT GROUP_CONCAT(name SEPARATOR ' + ') AS order_summary, SUM(price) AS total FROM product WHERE product_id IN (13, 15, 16);
+------------------------------------------------+-------+
| order_summary | total |
+------------------------------------------------+-------+
| Double Double + Animal Style Fries + Root Beer | 10 |
+------------------------------------------------+-------+

Answer 4

You can change the max length of the GROUP_CONCAT value by setting the group_concat_max_len parameter.
See details in the MySQL documantation.

Answer 5

There's a GROUP Aggregate function, GROUP_CONCAT.

Answer 6

In my case I had a row of Ids, and it was neccessary to cast it to char, otherwise, the result was encoded into binary format :
SELECT CAST(GROUP_CONCAT(field SEPARATOR ',') AS CHAR) FROM table

Answer 7

I had a more complicated query, and found that I had to use GROUP_CONCAT in an outer query to get it to work:
Original Query:
SELECT DISTINCT userID
FROM event GROUP BY userID
HAVING count(distinct(cohort))=2);
Imploded:
SELECT GROUP_CONCAT(sub.userID SEPARATOR ', ')
FROM (SELECT DISTINCT userID FROM event
GROUP BY userID HAVING count(distinct(cohort))=2) as sub;
Hope this might help someone.

Answer 8

Use MySQL(5.6.13) session variable and assignment operator like the following
SELECT #logmsg := CONCAT_ws(',',#logmsg,items) FROM temp_SplitFields a;
then you can get
test1,test11

Answer 9

For somebody looking here how to use GROUP_CONCAT with subquery - posting this example
SELECT i.*,
(SELECT GROUP_CONCAT(userid) FROM favourites f WHERE f.itemid = i.id) AS idlist
FROM items i
WHERE i.id = $someid
So GROUP_CONCAT must be used inside the subquery, not wrapping it.

Answer 10

Try this:
DECLARE #Hobbies NVARCHAR(200) = ' '
SELECT #Hobbies = #Hobbies + hobbies + ',' FROM peoples_hobbies WHERE person_id = 5;
TL;DR;
set #sql='';
set #result='';
set #separator=' union \r\n';
SELECT
#sql:=concat('select ''',INFORMATION_SCHEMA.COLUMNS.COLUMN_NAME ,''' as col_name,',
INFORMATION_SCHEMA.COLUMNS.CHARACTER_MAXIMUM_LENGTH ,' as def_len ,' ,
'MAX(CHAR_LENGTH(',INFORMATION_SCHEMA.COLUMNS.COLUMN_NAME , '))as max_char_len',
' FROM ',
INFORMATION_SCHEMA.COLUMNS.TABLE_NAME
) as sql_piece, if(#result:=if(#result='',#sql,concat(#result,#separator,#sql)),'','') as dummy
FROM INFORMATION_SCHEMA.COLUMNS
WHERE
INFORMATION_SCHEMA.COLUMNS.DATA_TYPE like '%char%'
and INFORMATION_SCHEMA.COLUMNS.TABLE_SCHEMA='xxx'
and INFORMATION_SCHEMA.COLUMNS.TABLE_NAME='yyy';
select #result;

Answer 11

Here, my intension was to apply string concatenation without using group_concat() function:
Set #concatHobbies = '';
SELECT TRIM(LEADING ', ' FROM T.hobbies ) FROM
(
select
Id, #concatHobbies := concat_ws(', ',#concatHobbies,hobbies) as hobbies
from peoples_hobbies
)T
Order by Id DESC
LIMIT 1
Here
select
Id, #concatHobbies := concat_ws(', ',#concatHobbies,hobbies) as hobbies
from peoples_hobbies
will return
Id hobbies
1 , shopping
2 , shopping, fishing
3 , shopping, fishing, coding
Now our expected result is at third position. So I am taking the Last row by using
Order by Id DESC
LIMIT 1
Then I am also removing the First ', ' from my string
TRIM(LEADING ', ' FROM T.hobbies )

Answer 12

we have two way to concatenate columns in MySql
select concat(hobbies) as `Hobbies` from people_hobbies where 1
Or
select group_concat(hobbies) as `Hobbies` from people_hobbies where 1

Answer 13

It is late but will helpfull for those who are searching "concatenate multiple MySQL rows into one field using pivot table" :)
Query:
SELECT pm.id, pm.name, GROUP_CONCAT(c.name) as channel_names
FROM payment_methods pm
LEFT JOIN payment_methods_channels_pivot pmcp ON pmcp.payment_method_id = pm.id
LEFT JOIN channels c ON c.id = pmcp.channel_id
GROUP BY pm.id
Tables
payment_methods
id | name
1 | PayPal
channels
id | name
1 | Google
2 | Faceook
payment_methods_channels_pivot
payment_method_id | channel_id
1 | 1
1 | 2
Output:

Answer 14

In sql server use string_agg to pivot a row field values into a column:
select string_agg(field1, ', ') a FROM mytable
or
select string_agg(field1, ', ') within group (order by field1 dsc) a FROM mytable group by field2

Answer 15

Another interesting example in this case -
Following is the structure of the sample table people_hobbies -
DESCRIBE people_hobbies;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int unsigned | NO | PRI | NULL | auto_increment |
| ppl_id | int unsigned | YES | MUL | NULL | |
| name | varchar(200) | YES | | NULL | |
| hby_id | int unsigned | YES | MUL | NULL | |
| hobbies | varchar(50) | YES | | NULL | |
+---------+--------------+------+-----+---------+----------------+
The table is populated as follows -
SELECT * FROM people_hobbies;
+----+--------+-----------------+--------+-----------+
| id | ppl_id | name | hby_id | hobbies |
+----+--------+-----------------+--------+-----------+
| 1 | 1 | Shriya Jain | 1 | reading |
| 2 | 4 | Shirley Setia | 4 | coding |
| 3 | 2 | Varsha Tripathi | 7 | gardening |
| 4 | 3 | Diya Ghosh | 2 | fishing |
| 5 | 4 | Shirley Setia | 3 | gaming |
| 6 | 1 | Shriya Jain | 6 | cycling |
| 7 | 2 | Varsha Tripathi | 1 | reading |
| 8 | 3 | Diya Ghosh | 5 | shopping |
| 9 | 3 | Diya Ghosh | 4 | coding |
| 10 | 4 | Shirley Setia | 1 | reading |
| 11 | 1 | Shriya Jain | 4 | coding |
| 12 | 1 | Shriya Jain | 3 | gaming |
| 13 | 4 | Shirley Setia | 2 | fishing |
| 14 | 4 | Shirley Setia | 7 | gardening |
| 15 | 2 | Varsha Tripathi | 3 | gaming |
| 16 | 2 | Varsha Tripathi | 2 | fishing |
| 17 | 1 | Shriya Jain | 5 | shopping |
| 18 | 1 | Shriya Jain | 7 | gardening |
| 19 | 3 | Diya Ghosh | 1 | reading |
| 20 | 4 | Shirley Setia | 5 | shopping |
+----+--------+-----------------+--------+-----------+
Now, a table hobby_list is generated having the list of all people and a list of each person's hobbies with each hobby in a new line -
CREATE TABLE hobby_list AS
-> SELECT ppl_id, name,
-> GROUP_CONCAT(hobbies ORDER BY hby_id SEPARATOR "\n")
-> AS hobbies
-> FROM people_hobbies
-> GROUP BY ppl_id
-> ORDER BY ppl_id;
SELECT * FROM hobby_list;

Answer 16

Use GROUP_CONCAT:
SELECT GROUP_CONCAT(hobbies) FROM peoples_hobbies WHERE person_id = 5;