如果Select inside SQL IN语句返回NULL，则选择ALL

Question

I'm trying to shorten my code and make it faster. However, I am struggling a bit with this statement. I want it to return all news if the value page_category is not set.

page_category is set in the DB as 1,2,3,4 and each news article has 1 category like below.

Page Category

News Category

I want to fetch each news article that has the category id within page_category .

This is my statement, and it works fine for whenever page_category is set.

"AND n.news_category IN (SELECT page_category FROM pages WHERE page_name = :pagename AND page_deleted IS NULL)";

How can I rewrite this so that n.news_category does not count if return is NULL ?

This is my whole current statement:

 $sql = "SELECT n.news_title, n.news_content, n.news_published_dt "
      . "FROM news n "
      . "LEFT JOIN languages l "
      . "ON n.news_lang = l.language_id "
      . "WHERE ((l.language_val = :language) OR (n.news_lang_all IS NOT NULL)) "
      . "AND n.news_deleted IS NULL "
      . "AND n.news_published = 1 "
      . "AND n.news_category IN (SELECT page_category FROM pages WHERE page_name = :pagename AND page_deleted IS NULL)";

Answer 1

Assuming that page_category takes on a NULL value and you want all rows in that case, then use exists instead:

EXISTS (SELECT 1
        FROM pages p
        WHERE p.page_name = :pagename AND p.page_deleted IS NULL AND
              (p.page_category is null or p.page_cateogry = n.news_category)
       )