id Subject mark Year
-------------------------
1 Maths 32 2008
1 Science 40 2009
1 Science 45 2008
1 English 50 2009
1 English 60 2008
我正在寻找这样的结果:
id Maths Science English
-----------------------------
1 32 40 & 45 50 & 60
请指教。我正在使用 MySQL。
最佳答案
作为@Mark suggested , GROUP_CONCAT()
可以给你以下结果:
SELECT id, subject, GROUP_CONCAT(mark SEPARATOR ' & ') marks
FROM results
GROUP BY id, subject;
+------+---------+---------+
| id | subject | marks |
+------+---------+---------+
| 1 | English | 50 & 60 |
| 1 | Maths | 32 |
| 1 | Science | 40 & 45 |
+------+---------+---------+
3 rows in set (0.00 sec)
来自这个测试用例:
CREATE TABLE results (id int, subject varchar(10), mark int);
INSERT INTO results VALUES (1, 'Maths', 32);
INSERT INTO results VALUES (1, 'Science', 40);
INSERT INTO results VALUES (1, 'Science', 45);
INSERT INTO results VALUES (1, 'English', 50);
INSERT INTO results VALUES (1, 'English', 60);
然而,另一种解决问题的方法是对每个主题使用 as 子查询:
SELECT r.id,
(SELECT GROUP_CONCAT(r_eng.mark SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'English' AND r_eng.id = r.id) English,
(SELECT GROUP_CONCAT(r_eng.mark SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Maths' AND r_eng.id = r.id) Maths,
(SELECT GROUP_CONCAT(r_eng.mark SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Science' AND r_eng.id = r.id) Science
FROM results r
GROUP BY r.id;
这将给出以下结果:
+------+---------+-------+---------+
| id | English | Maths | Science |
+------+---------+-------+---------+
| 1 | 50 & 60 | 32 | 40 & 45 |
+------+---------+-------+---------+
1 row in set (0.01 sec)
更新:
除了注释之外,您似乎需要考虑 year
字段。幸运的是,GROUP_CONCAT()
函数带有一个我们可以使用的 ORDER BY
子句。让我们从一个带有年份字段的新测试用例开始:
CREATE TABLE results (id int, subject varchar(10), mark int, year int);
INSERT INTO results VALUES (1, 'Maths', 32, 2008);
INSERT INTO results VALUES (1, 'Science', 40, 2009);
INSERT INTO results VALUES (1, 'Science', 45, 2008);
INSERT INTO results VALUES (1, 'English', 50, 2009);
INSERT INTO results VALUES (1, 'English', 60, 2008);
SELECT * FROM results;
+------+---------+------+------+
| id | subject | mark | year |
+------+---------+------+------+
| 1 | Maths | 32 | 2008 |
| 1 | Science | 40 | 2009 |
| 1 | Science | 45 | 2008 |
| 1 | English | 50 | 2009 |
| 1 | English | 60 | 2008 |
+------+---------+------+------+
5 rows in set (0.00 sec)
然后我们就可以使用 GROUP_CONCAT()
函数和 ORDER BY
子句,如下所示:
SELECT id,
subject,
GROUP_CONCAT(mark ORDER BY year SEPARATOR ' & ') marks,
GROUP_CONCAT(year ORDER BY year SEPARATOR ' & ') years
FROM results
GROUP BY id, subject;
+------+---------+---------+-------------+
| id | subject | marks | years |
+------+---------+---------+-------------+
| 1 | English | 60 & 50 | 2008 & 2009 |
| 1 | Maths | 32 | 2008 |
| 1 | Science | 45 & 40 | 2008 & 2009 |
+------+---------+---------+-------------+
3 rows in set (0.00 sec)
最后,要GROUP BY
水平行中的所有内容,我们可以使用我们在前面示例中使用的子查询技术:
SELECT r.id,
(SELECT GROUP_CONCAT(r_eng.mark ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'English' AND r_eng.id = r.id) English,
(SELECT GROUP_CONCAT(r_eng.year ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'English' AND r_eng.id = r.id) Years_English,
(SELECT GROUP_CONCAT(r_eng.mark ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Maths' AND r_eng.id = r.id) Maths,
(SELECT GROUP_CONCAT(r_eng.year ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Maths' AND r_eng.id = r.id) Years_Maths,
(SELECT GROUP_CONCAT(r_eng.mark ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Science' AND r_eng.id = r.id) Science,
(SELECT GROUP_CONCAT(r_eng.year ORDER BY year SEPARATOR ' & ')
FROM results r_eng
WHERE r_eng.subject = 'Science' AND r_eng.id = r.id) Years_Science
FROM results r
GROUP BY r.id;
这将返回以下内容:
+----+---------+---------------+-------+-------------+---------+---------------+
| id | English | Years_English | Maths | Years_Maths | Science | Years_Science |
+----+---------+---------------+-------+-------------+---------+---------------+
| 1 | 60 & 50 | 2008 & 2009 | 32 | 2008 | 45 & 40 | 2008 & 2009 |
+----+---------+---------------+-------+-------------+---------+---------------+
1 row in set (0.01 sec)
如果您希望标记和年份按降序排列,您可以在每个 ORDER BY year
之后简单地添加 DESC
关键字。
关于php - Mysql:如何将多行连接成具有不同字段名称的单行?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/3015786/