Question

我有一张桌子，里面装满了学生提交的不同项目。每个项目都应由三位不同的评委来评判。所以还有另一个分数表，其中包括projectid和judgeid。我正在尝试编写一个查询，可以选择任何尚未被判断过三次的项目。

以下是一些示例表......

项目

projectid | projectname
-----------------------
9         | Kintetics
11        | Volcano
15        | Robots
22        | Oceanlife

得分

scoreid (AI) | projectid | judgeid | score
------------------------------------------
1            | 9         | 15      | 5
2            | 11        | 15      | 18
3            | 9         | 23      | 12
4            | 11        | 23      | 11
5            | 9         | 45      | 19
6            | 22        | 15      | 3

我希望这个查询返回项目11,15和22，因为这三个人还没有分配给他们三名法官。

Answer 1

SELECT  a.ProjectID, a.ProjectName
FROM    Projects a
        LEFT JOIN Scores b
            ON a.ProjectID = b.ProjectID
GROUP   BY a.ProjectID, a.ProjectName
HAVING  COUNT(a.ProjectID) < 3

SQLFiddle Demo

要进一步了解联接，请访问以下链接：

Visual Representation of SQL Joins

输出

╔═══════════╦═════════════╗
║ PROJECTID ║ PROJECTNAME ║
╠═══════════╬═════════════╣
║        11 ║ Volcano     ║
║        15 ║ Robots      ║
║        22 ║ Oceanlife   ║
╚═══════════╩═════════════╝

Answer 2

另一种选择：

SELECT  a.ProjectID, a.ProjectName
FROM    Projects a
LEFT JOIN (select ProjectID, count(*) counted from Scores) b
       ON a.ProjectID = b.ProjectID
WHERE COALESCE(b.counted,0) < 3

Answer 3

SELECT COUNT(scores.id) AS score_count, projects.* 
FROM scores, projects
WHERE scores.projectid = projects.id
GROUP BY projects.id
HAVING score_count > 2

Answer 4

试试这个

select * from scores where id not in (select id from scores where project id in (select projectid from scores group by projectid having count(prjectid)=3))

Answer 5

试试这个：

SELECT * FROM Projects p WHERE (SELECT COUNT(*) FROM Scores s WHERE s.projectid = p.projectid) < 3

从一个表中选择在其他表中不存在三次的表

5 个答案: