MySQL display rows where value IS NULL or equal to X

Question

userPosts.value can contain one of two values: 0 or 1.

I am Left Joining userPosts to my Posts table.

I want to get all posts from my Posts table where userPosts.value = 0 as well as all posts that do not have any userPosts.value at all (thus, NULL).

The following only get me posts where value = 0 but no NULL:

SELECT * FROM $wpdb->posts
LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
WHERE userPosts.value != 1
ORDER BY $wpdb->posts.post_date DESC

The following only gets me posts where value = NULL:

SELECT * FROM $wpdb->posts
LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
WHERE userPosts.value IS NULL
ORDER BY $wpdb->posts.post_date DESC

but this yields no results at all:

SELECT * FROM $wpdb->posts
LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
WHERE userPosts.value = 0
AND userPosts.value IS NULL
ORDER BY $wpdb->posts.post_date DESC

and this does get me posts with value = 0 as well as NULL but it repeats all my NULL posts three times!

SELECT * FROM $wpdb->posts
LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
WHERE userPosts.value = 0
OR userPosts.value IS NULL
ORDER BY $wpdb->posts.post_date DESC

So what am I doing wrong?

Solution 1

Try to use parenthasis on OR condition (userContests.value = 0 OR userContests.value IS NULL)

 SELECT * FROM $wpdb->posts
    LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
    WHERE (userContests.value = 0
    OR userContests.value IS NULL)
    ORDER BY $wpdb->posts.post_date DESC

Solution 2

You partially answered your own question in the title: OR not AND, but try using DISTINCT:

SELECT DISTINCT * FROM $wpdb->posts -- Note "DISTINCT"
LEFT JOIN userPosts ON ($wpdb->posts.ID = userPosts.postID)
WHERE userContests.value = 0
OR userContests.value IS NULL -- Note "OR"
ORDER BY $wpdb->posts.post_date DESC

Solution 3

(x = 0) AND (x is NULL) - a single field cannot be two values at the same time. No surprise that you get no results at all, because you've specified a where condition that is impossible to satisfy.

As for the rest of the query. You use $wdpd->posts as your source table, but then use a table named userContests in the where clause. Does $wpdb->posts resolve to userContests? If so, why make the table name dynamic in one place and hard-coded it in another?