--- a/web/wp-includes/meta.php	Wed Dec 19 12:35:13 2012 -0800
+++ b/web/wp-includes/meta.php	Wed Dec 19 17:46:52 2012 -0800
@@ -123,9 +123,6 @@
 	if ( null !== $check )
 		return (bool) $check;
 
-	if ( ! $meta_id = $wpdb->get_var( $wpdb->prepare( "SELECT $id_column FROM $table WHERE meta_key = %s AND $column = %d", $meta_key, $object_id ) ) )
-		return add_metadata($meta_type, $object_id, $meta_key, $passed_value);
-
 	// Compare existing value to new value if no prev value given and the key exists only once.
 	if ( empty($prev_value) ) {
 		$old_value = get_metadata($meta_type, $object_id, $meta_key);
@@ -135,6 +132,9 @@
 		}
 	}
 
+	if ( ! $meta_id = $wpdb->get_var( $wpdb->prepare( "SELECT $id_column FROM $table WHERE meta_key = %s AND $column = %d", $meta_key, $object_id ) ) )
+		return add_metadata($meta_type, $object_id, $meta_key, $passed_value);
+
 	$_meta_value = $meta_value;
 	$meta_value = maybe_serialize( $meta_value );
 
@@ -711,7 +711,30 @@
 		$join = array();
 		$where = array();
 
-		foreach ( $this->queries as $k => $q ) {
+		$key_only_queries = array();
+		$queries = array();
+
+		// Split out the meta_key only queries (we can only do this for OR)
+		if ( 'OR' == $this->relation ) {
+			foreach ( $this->queries as $k => $q ) {
+				if ( ! isset( $q['value'] ) && ! empty( $q['key'] ) )
+					$key_only_queries[$k] = $q;
+				else
+					$queries[$k] = $q;
+			}
+		} else {
+			$queries = $this->queries;
+		}
+
+		// Specify all the meta_key only queries in one go
+		if ( $key_only_queries ) {
+			$join[]  = "INNER JOIN $meta_table ON $primary_table.$primary_id_column = $meta_table.$meta_id_column";
+
+			foreach ( $key_only_queries as $key => $q )
+				$where["key-only-$key"] = $wpdb->prepare( "$meta_table.meta_key = %s", trim( $q['key'] ) );
+		}
+
+		foreach ( $queries as $k => $q ) {
 			$meta_key = isset( $q['key'] ) ? trim( $q['key'] ) : '';
 			$meta_type = isset( $q['type'] ) ? strtoupper( $q['type'] ) : 'CHAR';
 
@@ -720,10 +743,35 @@
 			elseif ( ! in_array( $meta_type, array( 'BINARY', 'CHAR', 'DATE', 'DATETIME', 'DECIMAL', 'SIGNED', 'TIME', 'UNSIGNED' ) ) )
 				$meta_type = 'CHAR';
 
+			$meta_value = isset( $q['value'] ) ? $q['value'] : null;
+
+			if ( isset( $q['compare'] ) )
+				$meta_compare = strtoupper( $q['compare'] );
+			else
+				$meta_compare = is_array( $meta_value ) ? 'IN' : '=';
+
+			if ( ! in_array( $meta_compare, array(
+				'=', '!=', '>', '>=', '<', '<=',
+				'LIKE', 'NOT LIKE',
+				'IN', 'NOT IN',
+				'BETWEEN', 'NOT BETWEEN',
+				'NOT EXISTS'
+			) ) )
+				$meta_compare = '=';
+
 			$i = count( $join );
 			$alias = $i ? 'mt' . $i : $meta_table;
 
-			// Set JOIN
+			if ( 'NOT EXISTS' == $meta_compare ) {
+				$join[$i]  = "LEFT JOIN $meta_table";
+				$join[$i] .= $i ? " AS $alias" : '';
+				$join[$i] .= " ON ($primary_table.$primary_id_column = $alias.$meta_id_column AND $alias.meta_key = '$meta_key')";
+
+				$where[$k] = ' ' . $alias . '.' . $meta_id_column . ' IS NULL';
+
+				continue;
+			}
+
 			$join[$i]  = "INNER JOIN $meta_table";
 			$join[$i] .= $i ? " AS $alias" : '';
 			$join[$i] .= " ON ($primary_table.$primary_id_column = $alias.$meta_id_column)";
@@ -732,21 +780,12 @@
 			if ( !empty( $meta_key ) )
 				$where[$k] = $wpdb->prepare( "$alias.meta_key = %s", $meta_key );
 
-			if ( !isset( $q['value'] ) ) {
+			if ( is_null( $meta_value ) ) {
 				if ( empty( $where[$k] ) )
 					unset( $join[$i] );
 				continue;
 			}
 
-			$meta_value = $q['value'];
-
-			$meta_compare = is_array( $meta_value ) ? 'IN' : '=';
-			if ( isset( $q['compare'] ) )
-				$meta_compare = strtoupper( $q['compare'] );
-
-			if ( ! in_array( $meta_compare, array( '=', '!=', '>', '>=', '<', '<=', 'LIKE', 'NOT LIKE', 'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN' ) ) )
-				$meta_compare = '=';
-
 			if ( in_array( $meta_compare, array( 'IN', 'NOT IN', 'BETWEEN', 'NOT BETWEEN' ) ) ) {
 				if ( ! is_array( $meta_value ) )
 					$meta_value = preg_split( '/[,\s]+/', $meta_value );