mySQL 没有给出应有的结果

Question

我一直在为一项作业创建数据库，并且有一个需要实现的查询。 查询需要提供具有两个以上更新补丁的所有项目的项目 ID。 我正在使用查询:

SELECT projectID
FROM Transaction
HAVING COUNT(Transaction.status = ‘patch’) > 2

但我从中获得了 projectID 1，尽管唯一具有两个以上补丁的项目是 9。

我正在使用表格:

CREATE TABLE Transaction
( 
    transactionID SMALLINT NOT NULL,
    ProjectID SMALLINT NOT NULL,
    PRIMARY KEY(transactionID, projectID),
    FOREIGN KEY(projectID) REFERENCES Project(projectID),
    userID SMALLINT NOT NULL,
    FOREIGN KEY(userID) REFERENCES Developer(userID),
    date DATE NOT NULL,
    status ENUM('upload','update','patch') NOT NULL
);

这是我表中的数据:

INSERT INTO Transaction
(transactionID, projectID, userID, date, status) values

(1,1,2,'2013-12-29','upload'),
(2,7,8,'2014-05-12','update'),
(3,9,20,'2013-07-15','patch'),
(4,12,8,'2013-08-04','upload'),
(5,10,26,'2014-11-06','update'),
(6,9,26,'2013-07-04','patch'),
(7,20,26,'2012-12-15','upload'),
(8,13,14,'2013-02-16','update'),
(9,12,8,'2014-07-11','patch'),
(10,19,20,'2013-08-14','upload'),
(11,19,20,2013-02-13,'update'),
(12,14,20,'2013-11-10','patch'),
(13,18,14,'2012-12-26','upload'),
(14,1,2,'2014-07-14','update'),
(15,12,8,'2013-04-11','patch'),
(16,3,14,'2013-09-16','upload'),
(17,4,20,'2013-09-02','update'),
(18,9,20,'2014-09-18','patch'),
(19,8,14,'2013-03-24','upload'),
(20,17,8,'2014-10-20','update');

有人知道为什么这不起作用吗？

Answer 1

您缺少 group by 子句

按项目ID分组

SELECT projectID
   FROM Transaction
   where Transaction.status = 'patch'
   group by projectid
   HAVING COUNT(*) > 2