SQLite 中的 GROUP_CONCAT

Question

I am having data like this

1 A
1 B
1 C
1 D
2 E
2 F
3 G
3 H
3 I
3 J
3 K

by using this query

select ABSTRACTS_ITEM._id,Name 
from ABSTRACTS_ITEM , ABSTRACT_AUTHOR , AUTHORS_ABSTRACT
where
ABSTRACTS_ITEM._id = AUTHORS_ABSTRACT.ABSTRACTSITEM_ID
and
ABSTRACT_AUTHOR._id = AUTHORS_ABSTRACT.ABSTRACTAUTHOR_ID

Now, I want to show data like this

1 A,B,C,D
2 EF

and so on..I also know it can achieve by GROUP_CONCAT function. So, I tried with this

SELECT ABSTRACTS_ITEM._id,
GROUP_CONCAT(ABSTRACT_AUTHOR.NAME) FROM
(select ABSTRACTS_ITEM._id,
Name
from
ABSTRACTS_ITEM , ABSTRACT_AUTHOR , AUTHORS_ABSTRACT
where
ABSTRACTS_ITEM._id = AUTHORS_ABSTRACT.ABSTRACTSITEM_ID
and
ABSTRACT_AUTHOR._id = AUTHORS_ABSTRACT.ABSTRACTAUTHOR_ID)

But, It shows me error. So, what I am doing wrong here. What are the right procedure to achieve that?

Answer 1

You need to add GROUP BY clause when you are using aggregate function. Also use JOIN to join tables.

So try this:

SELECT AI._id, GROUP_CONCAT(Name) AS GroupedName
  FROM ABSTRACTS_ITEM AI 
  JOIN AUTHORS_ABSTRACT AAB ON AI.ID = AAB.ABSTRACTSITEM_ID
  JOIN ABSTRACT_AUTHOR AAU ON AAU._id = AAB.ABSTRACTAUTHOR_ID
 GROUP BY tbl._id;

See this sample SQLFiddle

---

What you were trying was almost correct. You just needed to add GROUP BY clause at the end. But the first one is better.

SELECT ID,
GROUP_CONCAT(NAME) 
FROM
    (select ABSTRACTS_ITEM._id AS ID,
     Name
     from
    ABSTRACTS_ITEM , ABSTRACT_AUTHOR , AUTHORS_ABSTRACT
    where
    ABSTRACTS_ITEM._id = AUTHORS_ABSTRACT.ABSTRACTSITEM_ID
    and
    ABSTRACT_AUTHOR._id = AUTHORS_ABSTRACT.ABSTRACTAUTHOR_ID)
GROUP BY ID;

Answer 2

Here my answer to this closed question (it has a good showcase in it). SQL group results by row

You must add an Aggregate Function to your selected field.
The one you want is: GROUP_CONCAT with a custom SEPARATOR ', '

See related MySQL Documentation: https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html

Your Select Query would look like this:

SELECT id_place, placename, GROUP_CONCAT(plant_name SEPARATOR ', ') AS 'plantnames'
FROM BLOOM
JOIN PLACE ON id_place = fk_place
JOIN PLANT ON id_plant = fk_plant
GROUP BY id_place, placename;

Then you get your desired output:

id_place	placename	plantnames
1	New York	orchid, tulip
2	London	rosebush, orchid, tulip
3	Paris	rosebush, lily, violet

Here is a DB Fiddle to check this out (MySQL 8.0): https://www.db-fiddle.com/f/sSU7G4kKEaxsLMNweAtLSA/2