to_ping query optimization

[misterbisson]

In wp-includes/comment.php, the following query requires a full table scan and can't be improved by adding an index:

<code>$trackbacks = $wpdb->get_results("SELECT ID FROM $wpdb->posts WHERE CHAR_LENGTH(TRIM(to_ping)) > 7 AND post_status = 'publish'");</code>

I can't see any obvious reasons why do_trackbacks would leave cruft in the to_ping field, and any cruft that may exist would get cleared after going through do_trackbacks again. So I'm proposing this replacement:

$trackbacks = $wpdb->get_results("SELECT ID FROM $wpdb->posts WHERE to_ping <> AND post_status = 'publish'");

[westi]

Checking through my live sites db - I have two posts with to_ping containing blank cruft.

[westi]

(In [6603]) Simplify to_ping query. Fixes #5649 props misterbisson.

[lloydbudd]

For reference: Andy Skelton asking him to submit the above patch, from [wp-hackers] to_ping query optimization

Hey Casey! Your query looks great to my eyes. I would guess that the
existing code was written to avoid selecting rows full of spaces or
shorter than '​http://' (7 chars). It would be more efficient to a) use
your query, and b) make sure the field is empty when all valid pings
have been sent.