Question

I have this mysql statement but I receive LIMIT in subquery error

SELECT  id
FROM    articles
WHERE  section=1 AND id NOT IN 
        (
        SELECT  id
        FROM    articles
        WHERE   is_top_story=1  ORDER BY timestamp DESC LIMIT 2
        )

I want to select all id-s from table where section=1 and id-s not in my inner(second) statement

+--id--+section+-is_top_story-+--timestamp--+
|  54  |   1   |     1        |    130      |
|  70  |   2   |     0        |    129      |      
|  98  |   3   |     1        |    128      |
|  14  |   1   |     1        |    127      |
|  58  |   4   |     0        |    126      |
|  13  |   3   |     1        |    125      |
|  64  |   1   |     1        |    124      |
|  33  |   1   |     1        |    123      |

My sql should return 64 and 33(they are with section=1 and is_top_story=1), because 54 and 14 (are in inner statment)

If any can give me some code I will be very grateful

Thanks

Answer 1

How about this:

SELECT a.id, a.times
  FROM articles AS a
  LEFT JOIN (
       SELECT id
         FROM articles
        WHERE is_top_story =1
     ORDER BY times DESC LIMIT 2) AS ax
  USING (id)
WHERE section = 1 AND ax.id IS NULL;

Join is a usual workaround when you need limits in subqueries; need for excluding logic just adds these ‘left join – joined.id IS NULL` parts to query. )

UPDATE: Got a bit confused by your example. The original query you’ve quoted was “take some articles with section = 1, then take out those that belong to the 2 most recent top_stories”. But in your example the section should also be taken into account when selecting these stories-to-ignore-…

It’s actually quite easy to update my query with that condition as well: just replace

WHERE is_top_story = 1

with

WHERE is_top_story = 1 AND section = 1

… but I think it might be even better solved at the client code. First, you send a simple query, without any joins whatsoever:

    SELECT id, is_top_story 
      FROM articles 
     WHERE section = 1
  ORDER BY times DESC;

Then you just walk through the fetched rowset, and just ignore two first elements with ‘is_top_story’ flag on, like that:

  ...
  $topStoriesToIgnore = 2;
  foreach ($rowset as $row) {
    if ($row->is_top_story && $topStoriesToIgnore-- > 0) {
      continue;  
    }
    // actual processing code goes here
  }