Question

So, I want to apply a WHERE condition to a field assigned by a COUNT() AS clause. My query currently looks like this:

SELECT new_tags.tag_id
       , new_tags.tag_name
       , new_tags.tag_description
       , COUNT(DISTINCT new_tags_entries.entry_id) AS entry_count 
FROM (new_tags) 
JOIN new_tags_entries ON new_tags_entries.tag_id = new_tags.tag_id 
WHERE `new_tags`.`tag_name` LIKE '%w' 
AND `entry_count` < '1' 
GROUP BY new_tags.tag_id ORDER BY tag_name ASC

The bit that’s failing is the entry_count in the WHERE clause – it doesn’t know what the entry_count column is. My table looks like this:

new_tags {
    tag_id INT
    tag_name VARCHAR
}

new_tags_entries {
    tag_id INT
    entry_id INT
}

I want to filter the results by the number of distinct entry_ids in new_tags_entries that pertain to the tag ID.

Make sense?

Thanks in advance.

Answer 1

To filter on aggegated values use the HAVING clause…

SELECT  
   new_tags.tag_id, new_tags.tag_name,  
   new_tags.tag_description,  
   COUNT(DISTINCT new_tags_entries.entry_id) AS entry_count  
FROM (new_tags)  
JOIN new_tags_entries ON new_tags_entries.tag_id = new_tags.tag_id   
WHERE `new_tags`.`tag_name` LIKE '%w'   
GROUP BY new_tags.tag_id  
HAVING COUNT(DISTINCT new_tags_entries.entry_id)  < '1' 
ORDER BY tag_name ASC