mysql JOIN查询多次返回相同的行

Question

我正在尝试显示从扇区1构建的所有通用坡度（来自game_slopes ）（即存在于game_created_slopes ）并且status_id = 1。

CREATE TABLE `game_created_slopes` (
  `id_created_slopes` int(11) NOT NULL,
  `id_player` int(11) NOT NULL,
  `id_slope` int(11) NOT NULL,
  `custom_name` varchar(45) DEFAULT NULL,
  `slope_condition` int(3) NOT NULL,
  `id_status` int(11) NOT NULL,
  `end_construction` datetime NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `game_created_slopes` (`id_created_slopes`, `id_player`, `id_slope`, `custom_name`, `slope_condition`, `id_status`, `end_construction`) VALUES
(168, 46, 6, 'Slope 24', 50, 1, '2016-05-17 17:01:25'),
(170, 46, 1, 'Slope 1', 1, 1, '2016-06-06 18:35:22'),
(172, 46, 7, 'Slope 3', 100, 1, '2016-06-08 21:48:43');


CREATE TABLE `game_slopes` (
  `id_slope` int(11) NOT NULL,
  `id_sector` int(11) NOT NULL,
  `name_english` varchar(45) NOT NULL,
  `name_french` varchar(45) DEFAULT NULL,
  `length` int(11) NOT NULL,
  `id_difficulty` int(11) NOT NULL,
  `cost` int(11) NOT NULL,
  `building_time` int(11) NOT NULL,
  `reputation` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `game_slopes` (`id_slope`, `id_sector`, `name_english`, `name_french`, `length`, `id_difficulty`, `cost`, `building_time`, `reputation`) VALUES
(1, 1, 'Slope 1', 'Piste 1', 2000, 1, 1000000, 13, 3000),
(6, 1, 'Slope 2', 'Piste 2', 1000, 2, 100000, 15, 5000),
(7, 2, 'Slope 3', 'Piste 3', 1400, 3, 200000, 5, 8000),
(8, 1, 'Slope 5', 'Piste 5', 1456, 4, 105000, 20, 5040);

不幸的是，应该返回的两个结果（ID 168和170） 每个都返回3次 。 我注意到，如果game_created_slopes包含5行，那么这两个ID将分别返回5次 。

（ID 172在扇区2中，因此未返回）

我的查询：

$this->db->distinct('game_slopes.id_slope, game_slopes.id_sector, game_created_slopes.id_slope, game_created_slopes.id_created_slopes, game_created_slopes.id_player');
$this->db->from('game_slopes, game_created_slopes');
$this->db->join('game_created_slopes as created_slopes_tbl', 'game_slopes.id_slope = created_slopes_tbl.id_slope', 'inner');
$this->db->where('created_slopes_tbl.id_status', '1');
$this->db->where('game_slopes.id_sector', '1);
$this->db->where('created_slopes_tbl.id_player', $currentUserID);
$query = $this->db->get();

PHP代码：

$num_slopes_for_this_sector = $this->Model->get_slopes_($currentUserID);

foreach ($num_slopes_for_this_sector->result() as $row){
      echo '<br>SECTOR :'. $i;
      echo '<br>id_created_slopes:'.$row->id_created_slopes;
}

我的查询出了什么问题？ 它应该仅返回两个ID。

Answer 1

您应该在单个表中使用，因为在第二个表中使用join

 $this->db->from('game_slopes');

如果您离开两个表，则两个表都将获得笛卡尔积

Answer 2

要显示直接翻译，请逐行...

SELECT DISTINCT game_slopes.id_slope, game_slopes.id_sector, game_created_slopes.id_slope, game_created_slopes.id_created_slopes, game_created_slopes.id_player
FROM game_slopes, game_created_slopes
INNER JOIN game_created_slopes as created_slopes_tbl ON game_slopes.id_slope = created_slopes_tbl.id_slope
WHERE created_slopes_tbl.id_status = 1
AND game_slopes.id_sector = 1
AND created_slopes_tbl.id_player = $currentUserID
;

我会像这样更格式化（也删除了意外的交叉连接，并更新了使用的引用/别名）

SELECT DISTINCT game_slopes.id_slope, game_slopes.id_sector
   , created_slopes_tbl.id_slope, created_slopes_tbl.id_created_slopes
   , created_slopes_tbl.id_player
FROM game_slopes
    INNER JOIN game_created_slopes AS created_slopes_tbl 
       ON game_slopes.id_slope = created_slopes_tbl.id_slope
WHERE created_slopes_tbl.id_status = 1
   AND game_slopes.id_sector = 1
   AND created_slopes_tbl.id_player = $currentUserID
;

最后，尽管我对php并不完全熟悉； 我将$currentUserID替换为? 并将其转换为参数化查询。

---

不过，我是一个懒惰的打字员（后来当需要用子查询替换表时，请给别名起个帮助）。

SELECT DISTINCT gs.id_slope, gs.id_sector
   , gcs.id_slope, gcs.id_created_slopes
   , gcs.id_player
FROM game_slopes AS gs
    INNER JOIN game_created_slopes AS gcs
       ON gs.id_slope = gcs.id_slope
WHERE gcs.id_status = 1
   AND gs.id_sector = 1
   AND gcs.id_player = $currentUserID
;