How to Combine Multiple Values into a Single String in SQLite Using GROUP_CONCAT?

GROUP_CONCAT Function in SQLite

This article discusses the usage and implementation of the GROUP_CONCAT function in SQLite to achieve data grouping and concatenation.

Introduction

Suppose you have a table with columns _id and Name, and the data is stored as follows:

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

To obtain the desired result, where each unique _id has a concatenated list of associated Name values, as illustrated below:

1 A,B,C,D
2 EF

The GROUP_CONCAT function can be utilized to achieve this.

Implementation

There was a minor issue in the provided query. To correctly implement the GROUP_CONCAT function, you must:

• Specify GROUP BY Clause: When using aggregate functions like GROUP_CONCAT, a GROUP BY clause is required to group the results.
• Use JOIN for Table Relationships: Join the necessary tables on appropriate columns to establish relationships between them.

Therefore, the revised query that will produce the desired output is:

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 AI._id;

Alternative Syntax

Alternatively, you can also structure the query as follows:

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;

This alternative syntax first prepares a subquery to fetch the necessary data and then applies the GROUP_CONCAT function on the result.

Conclusion

By employing the GROUP_CONCAT function in SQLite in conjunction with the JOIN operation and GROUP BY clause, you can effectively group and concatenate values within a result set.

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