Question

suppose i have two tables. articles and comments.

when i am selecting columns from articles table, i also want to select the number of comments on the article in the same select statement… (suppose the common field between these two tables is articleid)

how do I do that? I can get it done, but I do not know if my way would be efficient, so i want to learn the right way.

Answer 1

Use:

   SELECT a.articleid, 
          COUNT(*) AS num_comments
     FROM ARTICLES a
LEFT JOIN COMMENTS c ON c.articleid = a.articleid
 GROUP BY a.articleid

Whatever columns you want from the ARTICLES table, you’ll have to define in the GROUP BY clause because they aren’t having an aggregate function performed on them.