Question

I have two tables

one is keywords [id | keyword | account] k
and one is templateKeywordLink [templateId | keywordId] tkl

What I want to do is get a result set with all keywords from the keywords table (where account = 1)

I also want to add another column called selected.

if k.id in (select templateId from templateKeywordLink) then selected should contain “selected”. else it should be null

Im wondering what the optimal query is to do this?

Answer 1

There are several ways to do this. One way is to do a left join against a query that returns the IDs of interest.

Note that most databases have more compact ways to do what I did with a CASE statement, but CASE is portable to any relational database you could want to use.

SELECT k.*
  , CASE
      WHEN tkl.id IS NULL
      THEN NULL
      ELSE 'selected'
    END as selected
FROM keywords k
  LEFT JOIN (
      SELECT DISTINCT templateId
      FROM templateKeywordLink
    ) as tkl
    ON k.id = tkl.templateId