mysql - Codeigniter Active Record/MySQL 查询 - group_by 导致仅返回一行

Question

我有以下查询:

$this->db
     ->select('SQL_CALC_FOUND_ROWS null as rows
        ,services.*
        ,service_categories.*
        ,categories.*
        ,table4.*', FALSE)
     ->from('services')
     ->where('services.user_id', $user_id)
     ->join('service_categories', 'service_categories.service_id = services.service_id')
     ->join('categories', 'categories.cat_id= service_categories.cat_id')
     ->join('table4', 'table4.service_id= services.service_id', 'left')
     ->group_by('services.service_id')
     ->order_by('services.service_id', 'DESC');

 $query = $this->db->get();

表格如下所示:

Table: services
------------------------------------------------
| service_id | other_service_columns | user_id |
-----------------------------------------------|
|     23     |       other data      |    14   |
|     24     |       other data      |    14   |
------------------------------------------------


Table: service_categories
---------------------------------------
| service_cat_id | cat_id | service_id|
---------------------------------------
|        1       |   924  |     23    |
|        2       |   863  |     23    |
|        3       |   506  |     24    |
|        4       |   510  |     24    |
---------------------------------------

Table: categories
---------------------
| cat_id | cat_name |
---------------------
|   924  | cleaning |
|   863  | washing  |
|   506  | drying   |
|   510  | scrubbing|
---------------------

表 4 可能没有任何结果，因此我正在执行左连接。但是，当我按 service_id 分组时，我没有从“service_categories”和“categories”表中获取所有相关类别 - 查询中仅返回一行。 group_concat 是答案吗？如果是这样，我不确定如何使用它来获取我需要的结果 - 即查询中返回的所有相关类别。请帮忙!

我需要能够通过使用 foreach 迭代查询结果来处理查询结果，以在 View 中生成如下内容:

--------------------------------------------------------
| Service ID | Other Service Data | Service Categories |
--------------------------------------------------------
|     23     | Data for Service 23| cleaning, washing  |
|     24     | Data for Service 24| drying, scrubbing  |
--------------------------------------------------------

Answer 1

更新:根据您的评论和更新的问题，您的基本 SQL 查询可能如下

SELECT s.*, q.categories, t4.*
  FROM services s LEFT JOIN
(
  SELECT sc.service_id, GROUP_CONCAT(c.cat_name) categories
    FROM service_categories sc JOIN categories c 
      ON sc.cat_id= c.cat_id
   GROUP BY sc.service_id
) q ON s.service_id = q.service_id LEFT JOIN table4 t4
    ON s.service_id = t4.service_id
 WHERE s.user_id = ?

示例输出:

| SERVICE_ID | OTHER_SERVICE_COLUMNS | USER_ID |       CATEGORIES |
-------------------------------------------------------------------
|         23 |            other data |      14 | cleaning,washing |
|         24 |            other data |      14 | drying,scrubbing |

Here is SQLFiddle demo

Now a possible version of CI code

$sql = "SELECT s.*, q.categories, t4.*
          FROM services s LEFT JOIN
        (
          SELECT sc.service_id, GROUP_CONCAT(c.cat_name) categories
            FROM service_categories sc JOIN categories c 
              ON sc.cat_id= c.cat_id
           GROUP BY sc.service_id
        ) q ON s.service_id = q.service_id LEFT JOIN table4 t4
            ON s.service_id = t4.service_id
         WHERE s.user_id = $user_id";
$query = $this->db->query($sql);
foreach ($query->result() as $row) {
   ...
}

原始问题的答案: 恕我直言，您的查询有几个问题

1. 您将结果集限制为唯一带有 WHERE 子句的 service_id。因此，GROUP BY services.service_id 和 ORDER BY services.service_id 没有任何意义。仅当您想要将值打包到分隔字符串并返回唯一的行时，GROUP_BY 才有意义。
2. 您没有使用 LIMIT，因此 SQL_CALC_FOUND_ROWS 也没有任何意义。

话虽如此，您的查询可能看起来像

$result = $this->db
     ->select('services.*
        ,service_categories.*
        ,categories.*
        ,table4.*', FALSE)
     ->from('services')
     ->join('service_categories', 'service_categories.service_id = services.service_id')
     ->join('categories', 'categories.cat_id= service_categories.cat_id')
     ->join('table4', 'table4.service_id= services.service_id', 'left')
     ->where('services.service_id', $service_id)
     ->get();

这里是SQLFiddle 演示