SQL query with CASE WHEN used in WP_query wordpress function - sql

Question

I have this SQL query: SELECT * FROM `wpgo_postmeta` WHERE `meta_key` = 'price' ORDER BY CASE WHEN meta_value REGEXP '^[0-9]+$' THEN 1 ELSE 0 END, meta*value+0 DESC; *that works for me but I need to convert it so it's used by the wordpress apply_filters function.
I have tried multiple things including this WordPress Query: ORDER BY CASE WHEN
But then it returns an empty list. I know the query works because I have tested it manually.
I also tried this and it looks like it should work, but I get an empty list as well.
$query_args['meta_key'] = 'fave_property_price';
$query_args['orderby'] = "CASE WHEN meta_value REGEXP '^[0-9]+$' THEN 1 ELSE 0 END, metavalue+0 DESC;";

Answer 1

It looks like you want your numeric meta_value results to appear after the non-numeric ones.
In SQL you can simplify your ORDER BY like this.
ORDER BY (meta_value REGEXP '^[0-9]+$'), meta_value DESC
It works because the output of Boolean comparison operations appear a 1 for true and 0 for false.The parentheses aren't strictly necessary but they make the code a bit easier to read.
But, you cannot just stuff this SQL style clause into a WP_Query() object. Replacing the ORDER BY clause is tricky.
Start by converting this into a WP_Query operation. Those things don't look a whole lot like pure SQL. You need something like this, not debugged.
$q = new WP_Query (
['meta_key' => 'price',
'order' => 'DESC',
'orderby' => 'meta_value_num',
]);
Then you'll get your posts in numeric order by price, with oddball results for non-numeric prices. Run this query and convince yourself you get the posts you want, even if not in the perfect order.
Only then, put a filter handler on the posts_orderby filter to put in your SQLish custom ordering clause. The post you referenced shows how to do that: WordPress Query: ORDER BY CASE WHEN
Use John Blackbourn's Query Monitor plugin to see what your query looks like in real life, after all the WP_Query code finishes assembling it. The correct use of query filters can sometimes be confusing.
If code is poetry then the WP_Query code is an occult spell invocation chant. Sigh.