wp query - Is meta_key used for ordering, filtering, or both?

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In testing I am getting inconsistent results when experimenting with the meta_key parameter on a fresh Wordpress install. I'm combining it with orderby and/or meta_value to understand ordering and filtering results.

Is the meta_key parameter used for ordering search results as mentioned here or is it used for filtering as mentioned here? In no case have I seen Wordpress use it for both features, but it would apply to one or the other inconsistently.

I am aware that I could filter by meta_query but that is not the scope of this question. I have examined the WP_Query->get_posts() method, and I see the exact steps used to construct the SQL (convoluted as it is) but the purpose of this question is to understand the intended behaviour and submit a patch if necessary.

I am testing using Wordpress version 4.9.1 (current up-to-date version), but I'm interested in all Wordpress 4.x versions and differences between them.

In testing I am getting inconsistent results when experimenting with the meta_key parameter on a fresh Wordpress install. I'm combining it with orderby and/or meta_value to understand ordering and filtering results.

Is the meta_key parameter used for ordering search results as mentioned here or is it used for filtering as mentioned here? In no case have I seen Wordpress use it for both features, but it would apply to one or the other inconsistently.

I am aware that I could filter by meta_query but that is not the scope of this question. I have examined the WP_Query->get_posts() method, and I see the exact steps used to construct the SQL (convoluted as it is) but the purpose of this question is to understand the intended behaviour and submit a patch if necessary.

I am testing using Wordpress version 4.9.1 (current up-to-date version), but I'm interested in all Wordpress 4.x versions and differences between them.

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Share Improve this question asked Dec 19, 2017 at 8:06 dotancohendotancohen 83911 gold badge99 silver badges2020 bronze badges

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Sorted by: Reset to default 1

Column meta_key is used for filtering and partially for ordering. Why partially? It is used for ordering only in combination with meta_value. Columns meta_key and meta_value are connected together like column name and column value in traditional table. For raw SQL select it would be possible to order posts by meta_key but from a practical point of view, do you order your SQL selects by column names?

Let's assume that we have custom post type event with meta_key _speakers and _attendants. I don't see point of ordering events by meta_key but I see point of ordering by _speakers value or _attendants value. To do this you have to make such a query.

$query = new WP_Query(array(
    'post_type' => 'event',
    'meta_key' => '_speakers',
    'orderby' => 'meta_value_num',
));

or

$query = new WP_Query(array(
    'post_type' => 'event',
    'meta_key' => '_attendants',
    'orderby' => 'meta_value_num',
));

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