The tables against which to JOIN.
This property is a nested array. Each entry is an array representing a single table against which to join. The structure of each entry is:
array( 'type' => $join_type (one of INNER, LEFT OUTER, RIGHT OUTER), 'table' => $table, 'alias' => $alias_of_the_table, 'condition' => $join_condition (string or Condition object), 'arguments' => $array_of_arguments_for_placeholders_in_the condition. 'all_fields' => TRUE to SELECT $alias.*, FALSE or NULL ot