wpdb::get_results( string|null $query = null, string $output = OBJECT ): array|null

User Contributed Notes

1. Skip to note 5 content

   fabianplaza 10 years ago

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   Example about how can you retrieve data from a table using get_results function:

   public function wpdocs_some_function( $some_parameter ) {
           global $wpdb;
           $results = $wpdb->get_results( 
                   $wpdb->prepare( "SELECT count( ID ) as total FROM {$wpdb->prefix}your_table_without_prefix WHERE some_field_in_your_table=%d", $some_parameter ) 
           );
   }

   Please, note that I have used %d assuming that $some_parameter is a int value.
2. Skip to note 6 content

   flimm 4 years ago

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   Don’t forget to handle the error case. Here is how to catch errors from get_results:

   global $wpdb;
   $result = $wpdb->get_results( "SELECT * FROM invalid query" );
   if ( $wpdb->last_error ) {
     echo 'wpdb error: ' . $wpdb->last_error;
   }
3. Skip to note 7 content

   Rodrigo Vieira Eufrasio da Silva 2 weeks ago

   You must log in to vote on the helpfulness of this noteVote results for this note: 0You must log in to vote on the helpfulness of this note

   When using OBJECT_K, the docs say “Duplicate keys are discarded” but don’t say WHICH row survives. Looking at the source:

   foreach ( $this->last_result as $row ) {
   $var_by_ref = get_object_vars( $row );
   $key = array_shift( $var_by_ref );
   if ( ! isset( $new_array[ $key ] ) ) {
   $new_array[ $key ] = $row;
   }
   }

   The FIRST row for each key wins, and every later row with the same key is discarded. This is the opposite of how a normal PHP loop assignment behaves ($array[$key] = $value repeated in a loop normally means “last write wins”), so it’s an easy assumption to get backwards.

   In practice, this means: if you query something like “the latest meta value per post” or “the newest row per user_id” and rely on OBJECT_K to collapse duplicates, the row you actually get back depends entirely on the order MySQL returns rows in — which is NOT guaranteed unless you explicitly ORDER BY.

   // WRONG: assumes the “latest” row wins, but SQL row order isn’t
   // guaranteed without ORDER BY, so this can silently return stale data.
   $latest_by_post = $wpdb->get_results(
   “SELECT post_id, meta_value FROM $wpdb->postmeta
   WHERE meta_key = ‘my_key’”,
   OBJECT_K
   );

   // RIGHT: since OBJECT_K keeps the FIRST row per key, order by the
   // field that determines “latest” in DESCENDING order, so the row you
   // want to keep is the first one MySQL returns for each post_id.
   $latest_by_post = $wpdb->get_results(
   “SELECT post_id, meta_value FROM $wpdb->postmeta
   WHERE meta_key = ‘my_key’
   ORDER BY meta_id DESC”,
   OBJECT_K
   );

   If your key column isn’t guaranteed unique in the result set and you don’t care which duplicate wins, this doesn’t matter — but if you do care (e.g. “most recent per group”), always pair OBJECT_K with an explicit ORDER BY, otherwise which row you get is essentially undefined behavior.
4. Skip to note 8 content

   Eduard Milushi 8 years ago

   You must log in to vote on the helpfulness of this noteVote results for this note: -2You must log in to vote on the helpfulness of this note

   The example below is using heredoc to write the query and then getting the result through $wpdb->get_result(). The second parameter ARRAY_A used on the function will tell to the function that we need the result to be an Array.

   $query = <<<SQL
   SELECT
          p.ID, m.meta_key, m.meta_value
   FROM
        $wpdb->posts p
        LEFT JOIN
        $wpdb->postmeta m ON p.ID = m.post_id
        WHERE
              p.post_type IN ( 'post', 'page' )
              AND p.post_status = 'publish'
              AND ( m.meta_key IN ( '_yoast_wpseo_title', '_yoast_wpseo_metadesc', '_yoast_wpseo_meta-robots-noindex', 
              '_yoast_wpseo_meta-robots-nofollow' )
              OR 1 = 1 )
   SQL;
           
   /** @var array $result this will give us the ID and the other meta_field if any of all post types selected */
   $result = $wpdb->get_results( $query, ARRAY_A );