Mysql 使用多个表创建有效查询

我正在尝试对站点搜索进行查询。我需要对这个查询做的是，我想根据搜索关键字选择四个主要列（导师、学院、科目、城市）。键入关键字时，查询必须检查这四个表，并需要显示这四个类别下的搜索结果。当显示搜索结果时，我需要添加一些值以生成有意义的搜索结果。例如：考虑显示导师类别下的导师作为搜索结果，我需要显示他/她的姓名、城市、个人资料图像等

是这样的

**Tutors** 
  tutor's name
  city
  profile image
**institutes** 
  institute's name
  city
  profile image 
**subjects**
  subject name
  category name which belong this subject
**cities** 
  city name
  district name which city belong etc... 

我试过像这样的东西

$q = "SELECT keyword, col, city_name, image_name, tutor_code 
        FROM (
            SELECT tutor_name AS keyword, 'Tutors' AS col, IFNULL(c1.city_name, '') city_name, IFNULL(ti.image_name, '') image_name, tutor_code FROM tutors AS t
            LEFT JOIN address a ON t.address_id = a.address_id
            LEFT JOIN city c1 ON a.city_id = c1.city_id 
            LEFT JOIN tutor_images ti ON t.tutor_id = ti.tutor_id AND ti.image_type = 'profile'
            UNION
            SELECT subject_name AS keyword, 'Subject' AS col, '' city_name, '' image_name, '' tutor_code FROM subjects 
            UNION
            SELECT city_name AS keyword, 'City' AS col, '' city_name, '' image_name, '' tutor_code FROM city
            UNION
            SELECT institute_name AS keyword, 'Institute' AS col, '' city_name, '' image_name, '' tutor_code FROM institutes AS i
            LEFT JOIN address a ON i.address_id = a.address_id
            LEFT JOIN city c2 ON a.city_id = c2.city_id 
            LEFT JOIN institute_images ii ON i.institute_id = ii.institute_id AND ii.image_type = 'profile'             
        ) s
      WHERE keyword LIKE '%$queryString%' 
      LIMIT 10";

此查询大约可以工作50%，但无法在100%内工作。问题是它不能在institutes类别下显示城市名称和个人资料图像，不能在cities和subjects字段下显示district name和category name。我还想知道，这种查询是无效的，它会浪费时间和资源吗

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多谢各位

UNION

尝试将所有

SELECT

查询的结果放入一个包含一组列名/数据类型的大表中。因此，所有

SELECT

语句的列数和每列的数据类型必须匹配。您已经在使用关键字了，这是一种用于分隔类型的有用策略。我认为您可以在正确的列中选择额外的数据来实现这一点

我认为你应该做的是尝试一下，衡量一下你的表现。然后并行地进行单独的数据库调用，得到结果并测量性能。我认为它们可以与第二种方法相比，更易于理解和维护。

尝试以下方法：

SELECT keyword, col, city_name, image_name, tutor_code, district_name, category_name 
FROM (
    SELECT tutor_name AS keyword, 'Tutors' AS col, IFNULL(c1.city_name, '') city_name,  
             IFNULL(ti.image_name, '') image_name, tutor_code, '' district_name, '' category_name 
    FROM tutors AS t 
    LEFT JOIN address a ON t.address_id = a.address_id 
    LEFT JOIN city c1 ON a.city_id = c1.city_id 
    LEFT JOIN tutor_images ti ON t.tutor_id = ti.tutor_id AND ti.image_type = 'profile' 
    UNION
    SELECT subject_name AS keyword, 'Subject' AS col, '' city_name, '' image_name, '' tutor_code, 
             '' district_name, c.category_name 
    FROM subjects s 
    LEFT JOIN category_subjects cs ON s.subject_id = cs.subject_id 
    LEFT JOIN category c ON cs.category_id = c.category_id 
    UNION
    SELECT city_name AS keyword, 'City' AS col, '' city_name, '' image_name, '' tutor_code, 
             district_name, '' category_name 
    FROM city 
    UNION
    SELECT institute_name AS keyword, 'Institute' AS col, IFNULL(c2.city_name, '') city_name, 
             IFNULL(ii.image_name, '')  image_name, institute_code tutor_code, '' district_name, '' category_name
    FROM institutes AS i 
    LEFT JOIN address a ON i.address_id = a.address_id  
    LEFT JOIN city c2 ON a.city_id = c2.city_id  
    LEFT JOIN institute_images ii ON i.institute_id = ii.institute_id AND ii.image_type = 'profile'             
) s
WHERE keyword LIKE '%$queryString%' 
LIMIT 10

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你能用样本数据来解释吗？我能得到一个没有sqlfiddle的解决方案吗？这是一个艰苦的工作，我必须与更多的表。感谢您的回复。但是你的回答我不清楚。所以你能用一个例子来详细说明一下吗。谢谢。你好@Saharsh Shah很高兴再次见到你。请稍候，我将检查此项我的类别名称来自类别表和类别主题表，其中有哪个主题属于哪个类别。同样，城市名称未选择为学院。不确定。我也使用相同的地址和城市表。但不是选择城市作为研究所，而是与导师合作。现在可以了。另一种情况是，我可以将查询第一行中的“导师代码”更改为成员代码吗