CREATE TABLE students(
id INT PRIMARY KEY,
NAME VARCHAR(11)
);
CREATE TABLE courses(
id INT PRIMARY KEY,
NAME VARCHAR(11)
);
CREATE TABLE scores(
sid INT,
cid INT,
score INT,
RIMARY KEY (sid,cid)
);
3表關聯查詢：
SELECT st.id,st.name,c.NAME course,sc.score FROM students st
LEFT JOIN scores sc ON st.id=sc.sid
LEFT JOIN courses c ON sc.cid=c.id
將課程分類轉為列名，其列值為分數：
SELECT t.id,t.name,
CASE course WHEN '語文' THEN score ELSE 0 END a,
CASE course WHEN '數學' THEN score ELSE 0 END b,
CASE course WHEN '英語' THEN score ELSE 0 END c,
CASE course WHEN '歷史' THEN score ELSE 0 END d
FROM
(SELECT st.id,st.name,c.NAME course,sc.score FROM students st
LEFT JOIN scores sc ON st.id=sc.sid
LEFT JOIN courses c ON sc.cid=c.id) t
對上表按人員id分組，並將分完組的個列分數相加，組合到一行中，並對行求和：
SELECT t2.id,t2.name,SUM(a) '語文',SUM(b) '數學',SUM(c) '英語',SUM(d) '歷史',SUM(a+b+c+d) '總分' FROM
(
SELECT t.id,t.name,
CASE course WHEN '語文' THEN score ELSE 0 END a,
CASE course WHEN '數學' THEN score ELSE 0 END b,
CASE course WHEN '英語' THEN score ELSE 0 END c,
CASE course WHEN '歷史' THEN score ELSE 0 END d
FROM
(SELECT st.id,st.name,c.NAME course,sc.score FROM students st
LEFT JOIN scores sc ON st.id=sc.sid
LEFT JOIN courses c ON sc.cid=c.id) t
) t2
GROUP BY t2.id;
