mysql - 如果值为 null 则忽略条件 MYSQL/Codeigniter

Question

我正在使用 MYSQL/Codeigniter。如果传递的值为空，MySQL 查询如何忽略条件，如下例:

function get_category($category_id = 0){

 return $this->db->query("SELECT * FROM {$this->table} c
                    INNER JOIN db_category_event ce 
                    ON ce.category_id = c.category_id
                    INNER JOIN db_event_type e
                    ON e.event_id = ce.event_id
                     WHERE c.category_id = {$category_id}
                    WHERE c.visible = 1 AND e.visible = 1")
            ->result();
  }

Answer 1

试试这个:

SELECT * 

FROM   {$this->table} c

       INNER JOIN db_category_event ce 
       ON ce.category_id = c.category_id

       INNER JOIN db_event_type e
       ON e.event_id = ce.event_id

WHERE   ({$category_id} IS NULL OR c.category_id = {$category_id})
        AND c.visible = 1 AND e.visible = 1

或者，如果参数被视为零，则这应该有效:

SELECT * 

FROM   {$this->table} c

       INNER JOIN db_category_event ce 
       ON ce.category_id = c.category_id

       INNER JOIN db_event_type e
       ON e.event_id = ce.event_id

WHERE   ({$category_id} = 0 OR c.category_id = {$category_id})
        AND c.visible = 1 AND e.visible = 1