Question

There might be an easy solution here, but it seems to have me tripped up. I’m trying to query a table based on an array of values in two columns. Here is the pertinent table structure and sample data

comment table
id, userId, articleId .... etc etc

article table
id, userId .... etc etc

Data:  UserIds = 3, 10.   ArticleIds = 1, 2

Let’s say I’m trying to find all the comments for a particular set of article IDs: 1,2

I can easily use this query

select * from comments WHERE articleId IN(1,2)

However, here is where it gets complex. I have a query that executes prior to the comments query that determines the appropriate article IDs. Those IDs are in an array. Also in an array are the corresponding user IDs for each article.

What I want to do now is query the comments table for only the articles in the array (1,2) AND only for those comments made by the original author (3, 10).

The simple query above will bring back all the comments for articleId 1 and 20. So for example I can’t figure out where to add another conditional that says onyl comments for articleId 1, 20 AND corresponding userId, 3, 10.

Any help or suggestions would be much appreciated!

Answer 1

I think the simplest way is to write:

SELECT comments.*
  FROM articles
  JOIN comments
    ON articles.id = comments.articleId
   AND articles.userId = comments.userId
 WHERE articles.id IN (1, 2)
;

The AND articles.userId = comments.userId clause is what enforces your “only for those comments made by the original author” requirement.

Alternatively, you can use an EXISTS clause:

SELECT *
  FROM comments
 WHERE articleId IN (1, 2)
   AND EXISTS
        ( SELECT 1
            FROM articles
           WHERE id = comments.articleId
             AND userId = comments.userId
        )
;

or a single-row subquery:

SELECT *
  FROM comments
 WHERE articleId IN (1, 2)
   AND userId =
        ( SELECT userId
            FROM articles
           WHERE id = comments.articleId
        )
;