What is the difference between RELATION “AND” and “OR” in TAX_QUERY?

2 comments

1. tax_query is a 2-dimensional array, each sub-array can be considered to be a taxonomy query, typical its of the form:

   array(
     'taxonomy' => 'people',
     'field' => 'slug',
     'terms' => 'bob'
   )
   

   (e.g. posts in with the term with slug ‘bob’, of the ‘people’ taxonomy).

   The fact that tax_query is a two dimensional array means that you can have multiple taxonomy queries. In this case you may want to return posts which match all taxonomy queries (relation => 'AND' ) or posts which match at least one taxonomy query (relation => 'OR' ).

   As the codex:
   states

   This construct allows you to query multiple taxonomies by using the relation parameter in the first (outer) array to describe the boolean relationship between the taxonomy queries.

   For example:

   $args = array(
       'post_type' => 'post',
       'tax_query' => array(
           'relation' => 'AND', //Must satisfy all taxonomy queries
           array(
               'taxonomy' => 'movie_genre',
               'field' => 'slug',
               'terms' => 'action'
           ),
           array(
               'taxonomy' => 'actor',
               'field' => 'id',
               'terms' => array( 103, 115, 206 ),
               'operator' => 'NOT IN'
           )
       )
   );
   $query = new WP_Query( $args );
   

   returns all posts with move_genre term with slug ‘action’ AND does not have the actor terms with IDs 103,115,206.

   On the other hand (notice relation change):

   $args = array(
       'post_type' => 'post',
       'tax_query' => array(
           'relation' => 'OR',//Must satisfy at least one taxonomy query
           array(
               'taxonomy' => 'movie_genre',
               'field' => 'slug',
               'terms' => 'action'
           ),
           array(
               'taxonomy' => 'actor',
               'field' => 'id',
               'terms' => array( 103, 115, 206 ),
               'operator' => 'NOT IN'
           )
       )
   );
   $query = new WP_Query( $args );
   

   returns all posts with either have move_genre term with slug ‘action’ OR do not have the actor terms with IDs 103,115,206 (or satisfy both).

2. With AND the returned posts must have both terms.

   With OR the returned posts need only have one or the other.

   If they are returning the same then your posts you are querying probably all have both terms.

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