Understanding the ‘AND’ Operator in WordPress WP_Query’s tax_query

They are all convoluted ways of saying the same thing. Syntax 1 is the least efficient method, purely because it takes longer to type and uses unnecessary IN clauses when a single clause will do.

All 3 syntaxes are asking WP for posts that have been assigned to both category 76 and 78

Note that if they are not the same as this:

// NOT the same
$wp_query = new WP_Query(array(
    'post_type' => 'post',
    'tax_query' => array(
        array(
            'taxonomy' => 'category',
            'field' => 'id',
            'terms' => array(76, 78),
            'operator' => 'IN',
        ),
    ),
));

Why are there 3 ways of doing it though?

• syntax 1: is basically syntax 2 but more verbose. Part of this is that you’re trying to define conditions, and just like human language there’s more than one way to write the same thing
• syntax 2: if I were going to write this, this is close to how I’d write it, I’d probably add a post status of publish and add other parameters to try and constrain the search for performance
• syntax 3: category__and and the other top level parameters are there because they came first, and for backwards compatibility, as well as ease of use. If you look at the implementation of WP_Query you’ll see it gets converted into a tax_query clause. Note that these top level named conditions are less flexible and limiting compared to the tax_query equivalents.
  • you’ll also find that for custom taxonomies this becomes even more limiting as the only top level custom taxonomy variable available is deprecated and the documentation directs you to use tax_query