大多数匹配标签的 SQL 查询答案

【问题标题】：SQL query for most matching tags大多数匹配标签的 SQL 查询
【发布时间】：2016-01-31 09:07:55
【问题描述】：

让我们想象一下抽象数据库，它包含带有附加标签的对象（默认为多对多与附加表的关系）。现在，我们有一个用户，他想要找到与他提供的最多个标签匹配的对象，并按相关性排序。例如：

Object1: TagA, TagB, TagC, TagD
Object2: TagA,       TagC, TagD
Object3: TagB,             TagD, TagE, TagF
Object4: TagA, TagB, TagC,       TagE

用户请求 TagB、TagC、TagD 预期结果应如下所示：

Object1 (3 matches)
Object4 (2 matches)
Object2 (2 matches)
Object3 (1 match)

编辑： 示例结构（我在 SQLite 中创建它，但我们可以放心地假设为 MSSql）

CREATE TABLE Objects(Id int not null primary key, Name text);
CREATE TABLE Tags(Id int not null primary key, Name text);
CREATE TABLE ObjectTag(Id int not null primary key, ObjectId int, TagId int);

INSERT INTO Objects(Id, Name) VALUES (1, "Object1");
INSERT INTO Objects(Id, Name) VALUES (2, "Object2");
INSERT INTO Objects(Id, Name) VALUES (3, "Object3");
INSERT INTO Objects(Id, Name) VALUES (4, "Object4");

INSERT INTO Tags(Id, Name) VALUES (1, "TagA");
INSERT INTO Tags(Id, Name) VALUES (2, "TagB");
INSERT INTO Tags(Id, Name) VALUES (3, "TagC");
INSERT INTO Tags(Id, Name) VALUES (4, "TagD");
INSERT INTO Tags(Id, Name) VALUES (5, "TagE");
INSERT INTO Tags(Id, Name) VALUES (6, "TagF");

INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (1, 1, 1);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (2, 1, 2);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (3, 1, 3);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (4, 1, 4);

INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (5, 2, 1);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (6, 2, 3);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (7, 2, 4);

INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (8, 3, 2);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (9, 3, 4);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (10, 3, 5);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (11, 3, 6);

INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (12, 4, 1);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (13, 4, 2);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (14, 4, 3);
INSERT INTO ObjectTag(Id, ObjectId, TagId) VALUES (15, 4, 5);

预期结果（查询“TagB、TagC、TagD”）：

ObjectName | MatchCount
-----------+-----------
Object1    | 3
Object4    | 2
Object2    | 2
Object3    | 1

【问题讨论】：

您能分享一下您的表格结构吗？另外，你用的是什么rdbms？

标签： sql tags

【解决方案1】：

不确定您的表结构，但从您的帖子看来您可以使用GROUP BY 来实现这一点

select object, count(tag) as tagcount
from tags
where tag in ('TagB', 'TagC', 'TagD')
group by object;

【讨论】：

【解决方案2】：

这是一个答案：

SELECT t1.name, COUNT(t1.tag) as count FROM
    (SELECT o.Name as name, 
        1 as tag 
     FROM Objects AS o,
        ObjectTag AS ot 
     WHERE o.Id = ot.ObjectId 
         AND ot.TagId IN (2,3,4)) AS t1
     GROUP BY t1.name
     ORDER BY count DESC

【讨论】：