SQL JOIN with WHERE 條件當兩行的值相同並且一行匹配兩個不同的行

Question

我有這些表：

CREATE TABLE students(
  id int NOT NULL PRIMARY KEY,
  name VARCHAR(30) NOT NULL
 );

CREATE TABLE studentsActivities(
  studentId int NOT NULL,
  activity VARCHAR(30) NOT NULL,
  PRIMARY KEY (studentId, activity),
  foreign KEY (studentId) REFERENCES students(id) 
);

我必須返回所有打網球或足球的學生姓名。 但是，有一個我無法通過的測試用例，它是這樣說的：

同名學生。

我不知道測試用例的確切實現，但我懷疑是學生 A 叫 Carl 打網球，學生 B 也叫 Carl 打足球，Carl 出現兩次的情況。 我如何查詢該數據庫以獲得這樣的結果？ 我創建了演示庫來嘗試：

CREATE TABLE students(
  id int NOT NULL PRIMARY KEY,
  name VARCHAR(30) NOT NULL
 );

CREATE TABLE studentsActivities(
  studentId int NOT NULL,
  activity VARCHAR(30) NOT NULL,
  PRIMARY KEY (studentId, activity),
  foreign KEY (studentId) REFERENCES students(id) 
);

INSERT INTO students 
VALUES
(1, "Jeremy"),
(2, "Hannah"),
(3, "Luke"),
(4, "Frank"),
(5, "Sue"),
(6, "Sue"),
(7, "Peter");

INSERT INTO studentsActivities
VALUES
(1, "Tennis"),
(1, "Football"),
(2, "Running"),
(3, "Tennis"),
(4, "Football"),
(5, "Football"),
(6, "Tennis");

SQL 小提琴讓我們假設傳遞集是：

Jeremy 
Luke 
Frank 
Sue 
Sue

我已經嘗試過這兩個查詢，但沒有一個給出正確的答案。

--- 1
SELECT s.name
FROM students s
JOIN studentsActivities sa
ON sa.studentId = s.id
WHERE activity = "Tennis"
UNION
SELECT s.name
FROM students s
JOIN studentsActivities sa
ON sa.studentId = s.id
WHERE activity = "Football"
--- Returns Frank Jeremy Luke Sue (missing one Sue)

--- 2
SELECT s.name
FROM students s
JOIN studentsActivities sa
ON sa.studentId = s.id
WHERE activity = "Tennis"
OR activity = "Football"
ORDER BY s.name;
--- Returns Frank Jeremy Jeremy Luke Sue Sue (too much Jeremies)

Answer 1

您可以使用exists ：

select s.*
from students s
where exists (
    select 1 
    from studentsActivities sa 
    where sa.studentId = s.id and sa.activity in ('Tennis', 'Football')
)

DB Fiddle 上的演示：

id | name  
-: | :-----
 1 | Jeremy
 3 | Luke  
 4 | Frank 
 5 | Sue   
 6 | Sue   

Answer 2

加入表格，僅過濾包含您想要的活動的行並返回不同的行：

select distinct s.id, s.name
from students s inner join studentsActivities a
on a.studentId = s.id
where a.activity in ('Tennis', 'Football')

見演示。

結果：

| id  | name   |
| --- | ------ |
| 1   | Jeremy |
| 3   | Luke   |
| 4   | Frank  |
| 5   | Sue    |
| 6   | Sue    |

如果您只想要沒有 id 的學生姓名：

select s.name
from students s inner join studentsActivities a
on a.studentId = s.id
where a.activity in ('Tennis', 'Football')
group by s.id, s.name

見演示。

結果：

| name   |
| ------ |
| Jeremy |
| Luke   |
| Frank  |
| Sue    |
| Sue    |