if count value is null set it to zero - sql select statement

Question

Can't seem to get this working. If the count is null I want to set it to zero... else set it to the count. I am adding multiple counts in another part of my code so I cannot have null values when I do this.

$table = " ...

LEFT JOIN
    (SELECT user_id, IF(count(user_id) = '(null)',0,count(user_id)) as t1count
    FROM screenshot_logs
    GROUP BY user_id) as t_screenshots
        on t_screenshots.user_id = users.user_id
    ...

";

Answer 1

In the outer query, you can replace a NULL with a zero using the IFNULL() function, e.g.

SELECT ...
     , IFNULL(v.t1count,0) AS t1count
  FROM ...
  LEFT
  JOIN ( SELECT ... AS t1count
                ...
       ) v
    ON ...

---

The NULL you are getting returned by the outer query isn't from the inline view query. The NULL is a result of "no match" being found by the LEFT [OUTER] JOIN operation.

If you are referencing v.t1count in other expressions in the outer query, you can replace those references with NULLIF(v.t1count,0) as well.

Answer 2

The aggregate COUNT() will always return a value.

Reference: Does COUNT(*) always return a result?

Answer 3

You don't want to use = in there because null is != to everything. Try the ifNull() function.

http://dev.mysql.com/doc/refman/4.1/en/control-flow-functions.html#function_ifnull